ILLINOIS STATE GEOLOGICAL SURVEY 3 3051 00000 2240 Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/structuralreconn45krey J STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief BULLETIN NO. 45 STRUCTURAL RECONNAISSANCE OF THE MISSISSIPPI VALLEY AREA FROM OLD MONROE, MISSOURI, TO NAUVOO, ILLINOIS BY FRANK KREY In co-operation with Missouri Bureau of Geology and Mines PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 1924 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief BULLETIN NO. 45 ' STRUCTURAL RECONNAISSANCE OF THE MISSISSIPPI VALLEY AREA FROM OLD MONROE, MISSOURI, TO NAUVOO, ILLINOIS BY FRANK KREY In co-operation with Missouri Bureau of Geology and Mines PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS 1924 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief Committee of the Board of Natural Resources and Conservation A. M. Shelton, Chairman Director of Registration and Education Kendric C. Babcock Representing the President' of the Uni- versity of Illinois Edson S. Bastin Geologist (ii) 557 b no 45 .eft LETTER OF TRANSMITTAL State Geological Survey Division, February 23, 1924. A. M.'Shelton, Chairman, and Members of the Board of Natural Resources and Conservation: Gentlemen: I take pleasure in submitting herewith for publication the manuscript on the "Structural Reconnaissance of the Mississippi Valley Area from Old Monroe, Missouri, to Nauvoo, Illinois,'* with the recommendation that it be printed as Bulletin No. 45. In response to numerous inquiries from the oil industry regarding the geological structure of the area men- tioned above, a co-operative arrangement was made between the Missouri Bureau of Geology and Mines and the Illinois Geological Survey to undertake this work. The successful completion of this project is an illustration of how efficiently a geological problem, which knows no political boundaries, may be handled by co-operative effort. The work was assigned to Mr. Frank Krey who has brought the assignment to a satisfactory com- pletion. Respectfully yours, M. M. LEIGHTON, Chief. (in) CONTENTS Page Chapter I: — Introduction 5 Purpose 5 Location of area 5 Acknowledgments 5 Genera] statement 6 Methods employed 6 Degree of accuracy. . . 6 Manner of presentation 7 Chapter II. — Stratigraphy 15 General statement 15 Ordovician system 16 Jefferson City group 16 St. Peter group 17 Joachim dolomite 19 Plattin limestone 20 Kimmswick ("Trenton") limestone 21 Maquoketa shale 22 Silurian system 24 Alexandrian series 24 Edgewood formation 24 Sexton Creek limestone. 27 Devonian system 28 General statement 28 Distribution 29 Character of the rock and stratigraphic relations 29 Mississippian system 32 Lower Mississippian sub-system 32 Kinderhook series 33 Sweetland Creek (Grassy Creek) shale 33 Louisiana limestone 34 Hannibal shale 35 Chouteau limestone . . 37 Osage series 38 Fern Glen formation 38 Burlington-Keokuk limestone 38 Meramec series 39 Warsaw-Spergen formations 40 St. Louis and Ste. Genevieve formations 41 Pennsylvanian system 43 Tertiary system 44 Quaternary system 44 Chapter III. — Structure 45 General statement 45 Structural features 45 (1) ^ CONTENTS. Page Lincoln fold 46 Pittsfield-Hadley anticline 49 Western Adams County terrace 49 Southern Lincoln County syncline 49 Minor structures 50 Periods of deformation 50 Chapter IV. — Oil possibilities 54 Introduction 54 Previous exploration 54 Review of the principles of oil accumulation 55 Origin of oil 55 Migration of oil 55 Accumulation of oil 56 Combined effect of folding and erosion 57 Evidences of oil and gas within the region 57 Probable oil horizons 58 Factors affecting oil accumulation within the area 58 Structure 58 The Lincoln fold 59 Pittsfield-Hadley anticline 59 Adams County terrace or monocline 59 Minor structures 60 Effect of earlier periods of folding 60 Conclusion concerning structural factors 60 Stratigraphy 61 Kimmswick ("TreDton") limestone 61 Hoing sand 62 SiluriaD limestone and dolomite 62 Devonian limestone 62 Sweetland Creek (Grassy Creek) shale 62 Louisiana limestone 63 Kinderhook shale 63 Higher formations 63 Summary of conclusions 63 Chapter V. — Records of wells drilled in the Mississippi Valley area. ... 65 Records of wells located in Missouri 65 Clark County 65 Lewis County 66 Lincoln County 67 Marion County 68 Monroe County 70 Pike County 71 Ralls County 72 St. Charles County 73 Records of wells located in Illinois 74 Adams County 74 Calhoun County 75 Hancock County 76 Jersey County 77 Pike County 78 ILLUSTRATIONS Plate 1. Structure map of area immediately adjoining Mississippi River, In showing contours on the base of the Burimgton limestone pkt. 2. Longitudinal sections along Mississippi River, A-A on the Missouri In and B-B on the Illinois side pkt. 3. Three east-west cross-sections in the north, middle and south parts In of the area pkt. Facing Page 4. Generalized section of strata exposed in the area covered by the report 15 5. A. Steeply dipping Silurian limestone along the Cap-au- Gres fault, 6 miles west of Grafton, Jersey County, Illinois 24 B. Ledge of Noix oolite above Maquoketa shale in bed of creek on east side of road about 5 miles south of Hamburg 24 6. Sections taken at intervals along Grassy Creek, Pike County, Mis- souri. , 25 7. A. Limestone bluff on east side of Mississippi River valley, 4 miles south of Hamburg, showing unconformity between the Sexton Creek and underlying Bowling Green limestones 27 B. Brecciated St. Louis limestone northwest of St. Patrick, Mis- souri 27 8. East-west section across northern Ralls County 29 9. A. Unconformable contact between the Devonian and the over- lying Louisiana limestone in quarry about 3 miles south ol" Hardin , 34 B. Contact of Hannibal shale and Chouteau-Burlington limestone near Hardin in Calhoun County, Illinois 34 10. A. Steeply dipping Burlington-Chouteau limestone on the west limb of the Lincoln fold about 3 miles northeast of Silex 40 B. Lower Warsaw geode bed near Warsaw . % 40 11. A. Possible contact between Ste. Genevieve and underlying St. Louis limestones in old quarry northeast of Spanish Lake, Missouri 41 B. Tilted St. Louis limestone on the south limb of Lincoln fold, six miles west of Grafton, Jersey County, Illinois 41 12. Crossvsections to show the relation of the Cap-au-Gres fault to the Lincoln fold 47 13. Generalized north-south section of strata penetrated on the Mis- souri side of the Mississippi Valley area 49 (3) 4 ILLUSTRATIONS. Plate Facing Page 14. Generalized north-south section of strata penetrated on the Illinois side of the Mississippi Valley area 50 15. Section across Clark County, Missouri, and Hancock County, Illinois . , 51 16. Section across Marion County, Missouri, and Adams County, Illinois 52 17. Section across Pike County, Missouri, Calhoun and western Greene counties, Illinois 53 18. Diagrams showing conditions governing oil accumulation 57 TABLE 1. List of index numbers given on Plate I, including names of forma- tions and elevations of the tops of the formations where con- tacts are exposed 8 STRUCTURAL RECONNAISSANCE OF THE MISSISSIPPI VALLEY AREA FROM OLD MONROE, MISSOURI, TO NAUVOO, ILLINOIS By Frank Krey CHAPTER I— INTRODUCTION Purpose The work upon which this report is based was undertaken primarily to determine the presence of any prominent structural features along the Mississippi Valley which might be of im- portance in the development of the oil resources of the region. Careful observations were made of the different rock formations at their outcrops, their stratigraphic relations, their variations in lithologic character and thickness, and their distribution. The field work was done in the summer of 1922 from the early part of June to the early part of October, of which time seven weeks were spent in Missouri and the remainder in Illinois. The writer was assisted in the field by Messrs. George Ekblaw and A. H. Meyer, Mr. Ekblaw working from early June until the middle of September, when Mr. Meyer joined the writer and remained until the completion of the field season. Location of Area The area covered by this report includes all the counties of Illinois and Missouri immediately adjoining Mississippi River, beginning with St. Charles County, Missouri, and Jersey County, Illinois, on the south, and extending northward to the north boundary of Missouri and to the north boundary of Hancock County, Illinois (PI. I). Acknowledgments The writer wishes to acknowledge his indebtedness to Mr. F. W. DeWolf, formerly Chief of the Illinois State Geological Survey, and to Mr. H. A. Buehler, State Geologist of Missouri, for many helpful suggestions in planning the work. Thanks are (5) b MISSISSIPPI VALLEY AREA also due Messrs. Geo. Ekblaw and A. H. Meyer for their faithful and efficient help in the field. Observations along the Mississippi River bluff in Missouri between Winfield and Hannibal were made by Mr. Ebklaw. The publications of both the Illinois and Missouri Surveys have been freely drawn upon and different phases of the work have been discussed with members of the Illinois Geological Survey, particularly Drs. T. E. Savage and Stuarl Welier. General Statement It is obvious that the structure over much of the region, based as it is on comparatively few rather widely scattered ob- servations can be considered suggestive only so far as small local areas are concerned. The chief value of the work, therefore, is not its application to any one locality, but rather in furnishing a background and an understanding of the broad regional fac- tors without which the detailed work in small areas can not be rightly interpreted. Methods Employed Traverses along both the Illinois and Missouri bluffs of Mississippi River, and detailed observations on structure and stratigraphy at least once every mile, and generally oftener, comprised the data upon which this report is based. In addition to the bluff traverses, other east-west traverses were made across the counties at intervals of from two to three miles, but observa- tions were limited to only a few outcrops in a mile, and in some cases no exposures of rock were found for stretches of several miles. Elevations were obtained with a barometer or with a ba- rometer and topographic maps, and except for a month at the beginning of the work, the barometer was used in conjunction with a barograph. Degree of Accuracy The accuracy of the elevations varies somewhat at different localities. Where the barometer was used with topographic maps having contour intervals of twenty feet, the elevations are probably all correct to within twenty feet. On the other hand, where the barometer was used without the barograph and without the numerous checks afforded by a topographic map, the INTRODUCTION 7 elevations may not be correct within fifty feet. Fortunately the only area worked under such conditions was the whole of Lin- coln County and the southern part of Pike County, Missouri. When used wun the barograph, the barometer gave excellent results and numerous checks showed the elevations in all cases to be correct well within twenty-five feet. Topographic maps made by the Mississippi River Commission showing both bluffs, afforded data for the immediate valley of Mississippi- River and topographic maps were also available for most of Lewis, Clark and Marion counties, and parts of Pike, Lincoln, and St. Charles counties, Missouri. In Illinois, topographic maps were available for the southern tip of Calhoun county and small areas in Pike, Adams and Hancock counties. Manner of Presentation In presenting the results of this reconnaissance, as much in- formation as possible is placed upon the structure map of the region, (PL I) the structure being shown by means of contours on the base of the Burlington limestone. Outcrops are shown by appropriate symbols, given in the legend of PL I and are accom- panied by index numbers in each county. Table 1 lists under counties arranged alphabetically the index numbers designated on Plate I, the formation names, and the elevation of the tops of the formations where contacts are exposed. The major faults are indicated on Plate I. Areas in which detailed structural mapping has been done are outlined on the map. Approximate locations of all wells known to reach the Kimmswick ("Trenton") limestone are also shown. Variations in thickness and character of the formations are indicated by two longitudinal sections, (PL II) along Mississippi River, one (A-A) on the Missouri and the other (B-B) on the Illinois side, and by three east-west sec- tions across the area (PL III). The main body of the report is divided into three parts, the first dealing with the stratigraphy, the second with the structure, and a third with the oil possibilities. MISSISSIPPI VALLEY AREA Table 1. List of index numbers given on Plate I, including names of formations and elevations of the tops of the formations where contacts are exposed. Illinois Map number Formation Elevation on top of formation Map number Formation Elevation on top of formation Adams County 1 Keokuk Ft. above sea level 550 580 560 550 560 555 615 615 600 600 570 570 630 640 560 560 655 660 655 640 690 b b 625 660 600 620 625 650 680 620 430 b 680 Adams County 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Brown County 1 Calhoun County 1 2 3 4 5 6 7 8 9 10 11 11A 12 13 14 15 Keokuk Ft. above sea level 660 2 3 Warsaw-Spergen . . . Keokuk Warsaw-Spergen . . . Warsaw-Spergen . . . St. Louis 590 585 4 Keokuk 615 5 Keokuk a Keokuk 6 Keokuk Keokuk 520 7 Warsaw-Spergen . . . Hannibal 600 8 Warsaw-Spergen.. . Warsaw-Spergen . . . Warsaw-Spergen.. . Keokuk Keokuk b 9 10 11 12 a Warsaw-Spergen . . . Warsaw-Spergen . . a a a Keokuk Hannibal Hannibal a Silurian Hannibal 595 590 13 14 15 16 17 a Warsaw-Spergen . . . Warsaw-Spergen . . . Keokuk Keokuk b 525 485 18 19 20 21 22 23 24 Warsaw-Spergen . . . Warsaw-Spergen . . . Warsaw-Spergen . . . Warsaw-Spergen . . . a Keokuk Burlington Burlington Keokuk 450 600 25 26 Silurian Hannibal ....... Silurian 505 520 27 Keokuk 470 28 a Keokuk Silurian 455 29 Silurian 600 30 31 Keokuk a Keokuk Hannibal Hannibal 590 520 32 a Silurian 33 Keokuk Keokuk Keokuk Hannibal 455 34 Silurian b 35 36 Maquoketa Hannibal Maquoketa Silurian 490 600 37 38 Keokuk Keokuk b 500 INTRODUCTION Illinois — Continued Map number Calhoun County 16 17 18 19 20 21 22 22A 23 24 25 26 27 28 29 30 31 Hancock County 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Formation Maquoketa . Maquoketa. Silurian Kimmswick. Silurian Kimmswick . St. Peter . . . Maquoketa . Silurian Silurian Burlington. . St. Louis. . . St. Louis . . . St. Louis . . . St. Louis . . . St. Louis . . . St. Louis. . . Keokuk Keokuk Warsaw-Spergen . Warsaw-Spergen , Warsaw-Spergen , Keokuk Keokuk Keokuk Warsaw-Spergen . Warsaw-Spergen . a Warsaw- Warsaw- Warsaw- Warsaw- Keokuk Warsaw- Keokuk Warsaw- Keokuk Keokuk Warsaw- Warsaw ■Spergen , Spergen . Spergen . Spergen . Spergen, Spergen. Spergen . Spergen , Elevation on top of formation Ft. above sea level 560 570 490 480 565 520 540 b 460 510 b b b b b b b 565 560 625 620 610 580 555 570 625 615 605 605 645 640 545 595 565 580 550 535 615 590 Map number Hancock County 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 54A 55 56 57 58 59 60 61 62 63 64 65 66 Formation -Spergen . ■Spergen . -Spergen . -Spergen . Warsaw- Warsaw- Keokuk , Warsaw- Warsaw- Keokuk Warsaw-Spergen . Keokuk Keokuk Keokuk Keokuk Keokuk Keokuk a Keokuk Keokuk a a Keokuk Warsaw-Spergen . a a Keokuk Keokuk Warsaw-Spergen Keokuk Warsaw-Spergen Warsaw-Spergen a Keokuk a Keokuk Warsaw-Spergen Warsaw-Spergen Keokuk Warsaw-Spergen Warsaw-Spergen Keokuk Keokuk Warsaw-Spergen Warsaw-Spergen Elevation on top of formation Ft. above sea level 580 595 530 595 605 540 600 540 540 530 565 565 620 560 550 520 585 565 560 615 585 545 580 500 540 570 580 525 570 585 535 545 600 590 10 MISSISSIPPI VALLEY AREA Illinois — Continued Map number Hancock County 67 '68 69 70 71 72 73 74 75 J ersey County 1 2 3 4 5 6 7 Pike County 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Formation Warsaw- Warsaw- Warsaw- a a Warsaw- Keokuk Warsaw- Spergen . •Spergen . Spergen. Spergen Spergen Hannibal . . a Silurian Maquoketa Silurian . . . a Hannibal . . a Hannibal . Hannibal . Hannibal . Hannibal . Hannibal . Hannibal . Hannibal . a Burlington Hannibal . Hannibal . a Hannibal . Hannibal . Elevation on top of formation Ft. above sea level 570 580 580 580 540 565 500 500 580 520 450 590 540 520 585 555 620 550 b 575 655 765 605 Map number Pike County 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 Formation Hannibal . . a a Hannibal . . Hannibal . . a Hannibal . . Hannibal . . Hannibal . . Burlington. Burlington. Hannibal . . Hannibal. . Hannibal . . a a Hannibal . . Hannibal . . Silurian . . . Silurian . . . Hannibal . . Hannibal . . Hannibal . . Hannibal . . Hannibal . Hannibal . . Hannibal . . Hannibal . . Hannibal . . Hannibal . . Hannibal . . Hannibal . . Hannibal . . Maquoketa Hannibal . . Silurian . . . Silurian. . . . Silurian Elevation on top of formation Ft. above sea level 615 700 620 575 585 580 b b 460 600 575 600 615 495 500 620 580 590 550 550 510 460 475 475 520 545 570 595 505 600 545 505 480 INTRODUCTION Missouri 11 Map number Clark County 1 2 3 4 5 6 7 7a 8 9 10 11 12 13 14 15 Lewis County 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Formation Spergen Spergen Spergen Spergen Spergen Spergen Spergen Spergen Spergen Spergen Keokuk Warsaw- Warsaw- Warsaw- Warsaw- Keokuk Warsaw- Warsaw- Warsaw- Warsaw- Warsaw- Keokuk a Warsaw- Keokuk a Keokuk Warsaw-Spergen St. Louis St. Louis St. Louis St. Louis St. Louis Warsaw-Spergen Warsaw-Spergen a Warsaw-Spergen Hannibal a Keokuk Keokuk Keokuk Keokuk a Keokuk Keokuk Keokuk Keokuk. ...... Keokuk ....... Elevation on top of formation Ft. above sea level 550 595 575 560 580 520 600 b 605 580 600 520 590 535 580 600 b b b b b 590 580 590 b 530 535 555 b 585 530 b 570 580 Lincoln County 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Formation Plattin Plattin Kimmswick. Plattin St. Peter. . . Joachim . '. . . St. Peter . . . Plattin Plattin Plattin Maquoketa . Kimmswick. Kimmswick. Kimmswick . Kimmswick. Kimmswick. Plattin Kimmswick. Maquoketa . Hannibal . . . Maquoketa . Maquoketa. . Burlington. . Burlington. . Burlington. . Burlington. . Burlington. . Plattin Plattin Plattin St. Peter . . . Plattin a Plattin Plattin Burlington. . Joachim Kimmswick . Burlington. . Burlington. . Maquoketa . St. Peter. . . Elevation on top of formation Ft. above sea level 580 610 b 700 b 650 b 720 780 720 620 520 480 500 540 540 515 600 690 740 610 530 b b b b b b 600 690 700 610 630 730 b 580 630 1) 1) 640 660 12 MISSISSIPPI VALLEY AREA Missouri — Continued Map number Lincoln County 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 60A 61 62 63 64 65 66 67 68 69 70 71 Marion County 1 2 3 4 5 6 7 8 9 10 11 Formation Kimmswick Plattin Devonian Kimmswick Devonian Plattin Kimmswick Burlington Burlington Burlington a Kimmswick Plattin Joachim St. Peter St. Peter Plattin St. Peter (Cap-au Gres fault) St. Louis St. Louis Warsaw T -Spergen . vSt. Louis Warsaw-Spergen . Burlington St. Louis Warsaw r -Spergen . St. Louis a St. Louis Keokuk Burlington Burlington Burlington a a Burlington Burlington Burlington Burlington Hannibal Elevation on top of formation Ft. above sea level 780 740 780 620 720 510 640 b b b 650 b b b 670 680 b b b b b b b b 510 b 555 b b b b b b b 640 Map number Marion County 12 13 14 15 16 17 18 19 20 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Pike County 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Formation Hannibal. . Hannibal . . Hannibal . . a a Hannibal . . Hannibal . . Hannibal . . Burlington. Hannibal . . Hannibal . . Devonian. . Louisiana. . Louisiana. . Hannibal . . Louisiana. . a Louisiana. . Hannibal . . Hannibal . . Hannibal. . Hannibal . . a a Hannibal . . Louisiana.. . a Maquoketa . Kimmswick Devonian . . Louisiana. . Hannibal . . Maquoketa . Maquoketa . Hannibal. . Maquoketa . Maquoketa , Kimmswick Hannibal . . Louisiana. . Kimmswick Elevation on top of formation Ft. above sea level 640 560 515 500 530 b b 665 680 b 640 570 670 660 b b b b b 590 b 490 530 610 550 670 680 550 670 560 590 565 6S0 560 630 INTRODUCTION Missouri — Continued 13 Map number Formation Pike County 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 Ralls County 1 2 3 4 5 6 7 8 9 10 11 12 Maquoketa Hannibal. . a Hannibal . . Kimmswick Maquoketa , Maquoketa . Kimmswick Maquoketa . Maquoketa . a Maquoketa . a Maquoketa . Maquoketa . Kimmswick Plattin Maquoketa . Maquoketa . Hannibal . . Kimmswick Plattin Kimmswick Maquoketa . Maquoketa. Maquoketa . Louisiana. . Hannibal . . Hannibal . . Hannibal . . Maquoketa . Maquoketa . Maquoketa . Hannibal . . Hannibal . . Hannibal . . Kimmswick Kimmswick Elevation on top of formation Ft. above sea level 720 720 685 490 570 590 560 640 670 550 540 540 650 690 b b 700 670 ' 690 690 770 550 540 680 710 620 640 580 560 550 630 680 675 570 590 Map number Ralls County 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 Formation Kimmswick a Plattin Hannibal . . Kimmswick Devonian . . Hannibal . . Hannibal . . Hannibal . . Hannibal. . Hannibal . . Hannibal . . Burlington. Hannibal . . Hannibal . . a Burlington. Hannibal . . Louisiana. . Kimmswick Plattin Hannibal. . Maquoketa Kimmswick Plattin a Kimmswick Hannibal . . Hannibal. . Burlington. Burlington. Burlington. Hannibal . . Hannibal. . Burlington. Burlington. Burlington. Burlington. Burlington. Elevation on top of formation Ft. above sea level 610 580 580 580 640 680 650 590 615 605 610 b 585 585 b 620 620 635 490 670 560 580 550 500 610 640 b b b 600 650 b b b b b 14 MISSISSIPPI VALLEY AREA Missouri — Continued Map number St. Charles County 1 2 3 4 5 6 7 8 9 10 Formation Warsaw-Spergen Warsaw-Spergen Keokuk Keokuk. ...... Keokuk Keokuk a Keokuk Keokuk Warsaw-Spergen Elevation on top of formation Ft. above sea level 470 b b b b b b b 510 Map number St. Charles County 11 12 13 14 15 16 17 18 19 Elevation Formation on top of formation Ft. above sea level St. Louis b St. Louis b a Warsaw-Spergen . . . 520 Keokuk 490 Keokuk 460 a Hannibal 470 Kimmswick 460 a Well known to reach "Trenton." frLevel data not available. CHAPTER II— STRATIGRAPHY General Statement The succession of the stratified rocks which occur at the surface in this area includes formations ranging in age from Jef- ferson City of the Ordovician system to Carbondale of the Penn- sylvanian. Rocks older than those that outcrop are known from drill records and may be seen in outcrop on the flanks of the Ozarks to the southwest and in northern and central Wisconsin to the north, but inasmuch as these rocks are not known to con- tain petroleum and were not studied, they will not be discussed here. Plate IV shows a generalized section of the rocks exposed within the area in the northern and southern portions. Situated as this region is on the flanks of the old Paleozoic highlands of the Ozark region, the formations deposited during that time reflect to a greater degree the oscillations and shift- ings of the sea than do the strata lain down farther east toward the center of the Illinois basin. During periods of emergence, the associated slight warpings gave rise to local high and low areas so that during the periods of erosion, formations have been entirely eroded from the higher areas, but remained undisturbed in the low spots giving rise to unequal and irregular distribution. Furthermore, the extent to which the seas transgressed upon these highlands varied with different periods or even epochs. Some formations are thus seen to rest upon progressively older strata towards the Ozarks. Also, the variation in proximity of the shore line at different places made its influence felt on the character of the sediments so that the same formation may vary greatly in lithologic character in different localities. Some deposits lain down in bays from the main seas are found at the same elevations with older formations on both sides. The near-shore characteristics mentioned are especially pronounced for the Silurian, Devonian and early Lower Missis- sippian, but the area in which these formations come to the sur- face is limited to southern Calhoun and southwestern Jersey counties in Illinois and the eastern portions of Lincoln, Pike and Ralls counties in Missouri. Much detailed work needs to be done in this area before all the details of the complicated strati- graphic relations are known. Because the data will have to be (15) 16 MISSISSIPPI VALLEY AREA obtained from drill records and cuttings over much of this area, samples of cuttings from all deep holes should be carefully col- lected and logs be preserved. Ordovician System Formations of the Ordovician system outcrop along a belt 5 to 15 miles wide, extending from southwestern Jersey County westward across Calhoun County, Illinois, and thence across Mississippi Valley to eastern Lincoln County in Missouri. The southern limit of the belt of outcrop is terminated by a large fault (Cap-au-Gres) which juxtaposes rocks of Mississippian age with those of Ordovician age. In Missouri, the Ordovician rocks out- crop along a northward pitching arch which crosses eastern Lin- coln, Pike and Ralls counties, but disappear beneath younger formations before Marion County is reached. The formations exposed include the Jefferson City group, the St. Peter group, Joachim formation, Plattin formation, Kimmswick limestone, Fernvale limestone, and Maquoketa shale. JEFFERSON CITY GROUP The term "Jefferson City Group" is here used in the same sense as employed by Dake 1 and includes both Cotter and Powell formations as well as typical Jefferson City. Rocks referable to this group outcrop along the bluff and in the ravines cutting the bluff in Lincoln County, Missouri, from the Cap-au-Gres fault northward to within half a mile of Foley, a distance of about 2 miles. Other outcrops of this group were seen near the bottom of a large ravine north of the road near the center of sec. 4, T. 49 N., R. 2 E., and are reported from the south side of Sandy Creek in sec. 35, T. 50 N., R. 2 E., 2 from the Mississippi River bluff north of the Cap-au-Gres fault in Cal- houn County, Illinois. 3 Since both the "Jefferson City Group" and the overlying St. Peter group are below any known oil-bearing horizon in this region, no time was spent in detailed study of these formations. iDake, C L., The problem of the St. Peter sandstone; Missouri School of Mines and Metallurgy. Bulletin, Vol. VI., no. 1. p. 12, 1921. 'Potter. W. B., Geology of Lincoln County in preliminary report on iron ores and coal fields: Geological Survey of Missouri, 1872. •Weller. Stuart, Geology of southern Calhoun County, 111.: State Geol. Survey Bull. 4, p. 221. 1907. STRATIGRAPHY 17 As observed, the strata consist essentially of gray to buff, earthy, dolomitic limestone with interbedded sandy and cherty layers. The following section measured in the bluff about 1}4 miles south of Foley will serve to show the general character of the formation: Thickness Description of strata Feet Inches Limestone, dolomitic, gray, sandy 1 6 Limestone, white, earthy, in uneven beds 1 2 Limestone, gray, earthy, in uneven beds 2 6 Limestone, white, earthy, and knotty chert 1 6 Limestone, gray, sandy 2 — Limestone, dolomitic, white, earthy and laminated gray, regular beds 2 to 12 inches alternating with sandy layers 16 — Sandstone, gray, slightly calcareous 5 — Limestone, dark, porous, sandy, brecciated and cherty, uneven top surface 3 — Limestone, blue-gray, weathers brown; sandy and oolitic. . 1 — Dolomite, porous, brown, cherty at base (contorted and brecciated) 3 — Dolomite, dark blue gray, porous and finely granular, earthy at base 10 — Concealed to fiat 50 — The greatest exposed thickness of strata belonging to this group is about 130 feet. This formation, though outcropping only in a limited area, underlies the whole region. ST. PETER GROUP Heretofore, the massive sandstone above the "Jefferson City group" has in this area been considered a single stratigraphic unit and has been referred to as the saccharoidal or St. Peter sandstone. Recent work to the south in Ste. Genevieve and Jefferson counties, Missouri, however, shows the St. Peter group to consist of two formations, the massive St. Peter sandstone above, and dolomite and sandstone, together known as the Everton formation, below. In this area dolomitic beds have been observed in the middle portion of the St. Peter group and as the thickness of the St. Peter in this region is equal to the com- bined thickness of the St. Peter and Everton beds farther south, it is probable that both formations are also present here. Though outcropping over only a limited extent, the St. Peter group underlies the entire region; is a noted water carrier, and in the northern part of the region provides many artesian 18 MISSISSIPPI VALLEY AREA wells of fresh water which farther south becomes increasingly saline. In this area the top of the St. Peter group is considered the base of any probable oil production. The best exposures of this group are found in Lincoln County, Missouri, and Calhoun County in Illinois, and at least one ex- posure is known from Ralls County, Missouri. 4 In Lincoln County, the St. Peter group is prominent in the river bluffs from the Cap-au-Gres fault to about a mile north of Foley. It is also found along the ravines and creeks back from the bluff for a distance of 3 or 4 miles. Other outcrops of St. Peter were observed along Mill Creek and its tributaries in sees. 28 and 33, and near the head of Sandy Creek in sees. 4 and 9, T. 51 N., R. 1 W. In Calhoun County, Illinois, the St. Peter group outcrops in the Mississippi bluff between West Point and Dogtown land- ings, where it stands as a sheer bluff and does not lend itself to detailed study. Wherever observed, the St. Peter is a massive sandstone in- distinctly bedded or stratified. The color on the weathered surface is usually brown, but in protected places white or yellow. It is moderately coarse grained; the grains, the surfaces of which are frosted, are loosely cemented, well rounded, and of uniform size. Where the sandstone outcrops in the bed of streams and is subject to the action of running water and other forces of erosion, the bedding is more distinct, surfaces often ripple marked, and cross-bedding shown. At two localities dolomite was found interbedded with the sandstone. At the east point of the bluff about Yi mile south of Foley, a 6-foot bed of dolomite was ob- served, and in the ravine about a mile south of the last locality, many beds of dolomite 4 to 6 inches thick were found inter- layered with sandstone, below which more massive sandstone, showing ripple marks occurred. The stratigraphic relations of the St. Peter group to the underlying formations were not observed. The contact of the St. Peter with the overlying formation which was noted at several places, appears to be conformable, the St. Peter group apparently grading into the overlying Joachim dolomite. The thickness of the St. Peter group as developed in this area is be- tween 125 and 150 feet. *Shepard, E. M., Underground waters of Missouri; U. S. Geol. Survey Water Supply- Paper 195, p. 54, 1907. STRATIGRAPHY 19 JOACHIM DOLOMITE The Joachim 5 dolomite, also known as the first Magnesian limestone of the older writers is exposed as a narrow belt bordering the outcrops of St. Peter sandstone and is best exposed in Lincoln County, Missouri, and Calhoun County, Illinois, but local out- crops are also found in Ralls County, Missouri, namely near the south line of sec. 21, T. 55 N., R. 4 W., and near the town of Spaulding, sec. 25, T. 56 N., R. 6 W. Specific locations of ob- served outcrops in Lincoln County, Missouri, are in the Missis- sippi River bluff about Yi mile north of Foley; along Sandy Creek in the southwest corner of sec. 30 and S. }/£, sec. 32, T. 50 N., R. 2 E.; S. y 2 , sec. 7, T. 50 N., R. 1 E.; the SE J4, sec. 10, T. 50 N., R. 1 W., and near the head waters of Sandy Fork in the northwest portion of T. 51 N., R. 1 W. In Calhoun County, Illinois, the best exposure of Joachim is found at the abandoned quarry in the river bluff near West Point landing. As seen in the quarry in Calhoun County, the Joachim is a massive dolomite occurring in beds up to several feet thick. The color on the fresh surface is gray or yellow, but on the weathered face it is often brown. It is finely granular to crystalline, but some beds may be earthy and in the lower portion sandy. The lithologic characters of the rock are surprisingly uniform through- out its belt of outcrop, and it can easily be recognized by its yellowish color and finely granular to crystalline texture. Fos- sils are scarce, and wanting in most exposures. In Calhoun County, Illinois, the formation is approximately 75 feet thick, but in Lincoln County, Missouri, it is not much over 50 feet. The relation of the Joachim with the underlying St. Peter has already been discussed, and its relation to the over- lying Plattin appears to be unconformable. In Calhoun County the contact is more or less indistinct, and the formation appears to grade into the overlying Plattin limestone without any dis- tinct break. The upper beds of the Joachim, however, are some- what more argillaceous than the others. Westward in Lincoln County, Missouri, the Joachim is separated from the Plattin by a distinct shale several feet in thickness. The shale is not well developed in the bluff, but becomes increasingly prominent westward and reaches a thickness of about four feet in western 5 Winslow, Arthur, Lead and zinc deposits of Missouri: Mo. Geol. Survey, Vol. VI, 1st ser., p. 352, 1894. 20 MISSISSIPPI VALLEY AREA Lincoln County. It is green in color and in some places contains nodules of earthy limestone. A similar shale, also present at this horizon in Ralls County, Missouri, may be seen at the localities mentioned as having outcrops of the Joachim. At the outcrop near Spaulding in Ralls County the shale is distinctly sandy. PLATTIN LIMESTONE The Plattin 6 limestone overlying the Joachim, outcrops in the same general vicinity as that formation, but because of its greater thickness, it is exposed in a broader belt. In Lincoln County, Missouri, it outcrops for several miles from both sides of a line drawn from the river bluff half way between Apex and Foley northwestward to a point about 4 miles northeast of Louis- ville. Its outcrop in Pike County, Missouri, is limited to a small area near the south line of the county southwest of Edge- wood. In Ralls County, it outcrops at localities mentioned as having outcrops of Joachim. On the Illinois side of Mississippi River, it is exposed only in the river bluffs near West Point Land- ing in Calhoun County. Though somewhat variable in lithologic character, it is readily distinguishable from either the overlying or underlying formation. On the weathered surface the color is generally gray, but when freshly broken it is drab or bluish. It is massive with bedding often indistinct. The weathered surface is carious in many places, the pits varying in diameter from a fraction of an inch to more than a foot. The texture varies from granular to lithographic. Coarsely granular, fossiliferous beds are prom- inent in the lower 50 feet and in the upper portion. Dense, lithographic beds characterized by conchoidal fracture occur at different horizons throughout the formation, but are most abund- ant near the top and bottom. The larger part of the formation especially the central portion, consists of finely granular, dolo- mitic limestone, drab in color, but on closer examination an intimate mixture of earthy yellowish dolomite with the drab can be observed. The upper 10-15 feet of the Plattin wherever ex- posed, consists of layers 6 inches to 2 feet thick of dense, drab to blue, lithographic limestone, separated by partings Y± to 2 inches thick of drab, calcareous shale which is petroliferous, thin slivers of which burn when lighted with a match. The limestone •Buckley, E. R., and Buehler, H. A., The quarrying industry of Missouri: Missouri Bureau of Geology and Mines, Vol. II, 2nd. ser., p. Ill, 1904. STRATIGRAPHY 21 weathers white, and where it occurs in a bluff, it resembles strongly a wall of masonry. Where this horizon makes up the. surface rock, it weathers to a light, spongy, porous mass so soft it can be scratched with the finger-nail, and preserves beautifully the enclosed fossil forms. It is for this horizon that Rowley pro- posed the name Auburn Chert. 7 The thickness of the Plattin is not much less than 200 feet in Lincoln County, Missouri, for 180 feet may be seen in the bluff about 1H miles north of Foley. In Calhoun County, Illinois, it does not appear to be greater than 125 feet, and judging from well records, it probably thins out to the north. There is a suggestion also that where the Plattin is thickest the Joachim is thinnest and vice versa. KIMMSWICK ("TRENTON") LIMESTONE The Kimmswick 8 limestone which overlies the Plattin is best exposed in northeastern Lincoln County, a strip running northwest-southeast across central Pike County and in the gen- eral vicinity of New London in Ralls County, Missouri. In Illinois, the best exposures may be seen in the Mississippi River bluff in the vicinity of Batchtown and along the Illinois River bluff in southwestern Jersey County. Lithologically, the Kimmswick is essentially a gray, some- times tinted blue or pink, coarsely granular limestone. Locally, however, especially in the upper portion there is found consider- able variation. Where the Cap-au-Gres fault intersects the bluff in Lincoln County, the upper 6 feet of the Kimmswick con-' sists of dense, massive, hard, finely granular limestone, some- what porous, which on weathering shows a knotty character and is mottled pink and gray. Similar limestone of like thick- ness is found capping the Kimmswick along Missouri River about \y Ledge of Noix oolite above Maquoketa shale in bed of creek on east side of road about 5 miles south of Hamburg, Calhoun County, Illinois. Illinois State Geological Survey. Feet 200 yards downstream ran o l o J-QJ o I o ran o I o Dolomite, massive, brown. (Bowling Green dolomite) Limestone, granular, in beds 2-6 inches. Separated by shale partings 1/4 to 1 inch thick. (Cyrene limestone) Oolite, granular, fossiliferous. (Noix oolite) Limestone, bluish, earthy, magnesian (abundant Edgewood corals) Shale, blue-grey (Maquoketa) Bulletin Xo. 45, Plate VI. 400 yards downstream Dolomite, massive, brown. (Bowling Green dolomite) Limestone, massive, coarsely granular and crystalline. Cyrene limestone - — I - Limestone, thin, shaly. 'EIErEE: Shale, blue-grey. =-= (Maquoketa) Sections taken at intervals along Grassy Creek, Sec. 24, T. 54 N., R. 3 W., Pike County, Missouri. STRATIGRAPHY 25 and limestone below. A portion of the Gyrene member which is oolitic is called the Noix oolite. Savage 12 considers the oolite equivalent to the upper portion of the Cyrene. The upper portion of the Edgewood (Bowling Green mem- ber) is a lithologic unit throughout the area, but the lower por- tion shows considerable variation. At most exposures, the Noix oolite constitutes the basal Silurian formation, and rests directly on Maquoketa shale (PL V, B), although in Grassy Creek in sec. 24, T. 54 N., R. 3 W., the Noix oolite is separated from the Maquoketa by from 1 to 3 feet of earthy, magnesian limestone which is abundantly fossiliferous. In general, it may be said that the Noix oolite forms the basal formation of the Silurian in the vicinity of the river bluffs on both Illinois and Missouri sides. Locally, however, as in southern Calhoun County and along Grassy Creek in sec. 24, T. 54 N., R. 3 W., of Pike County, Missouri, the basal Silurian formation is a coarsely crystalline, gray fossiliferous limestone. Eastward in Jersey County, Il- linois, no Noix oolite was seen, and westward in Missouri near Bowling Green and Cyrene in Pike County and northwestern Lincoln County, the basal Silurian is a fossiliferous, earthy, mag- nesian limestone up to 20 feet thick and no Noix oolite appears to be present. In the southeast corner sec. 13, T. 53 N., R. 3 W., near Bowling Green, about 3 feet of earthy, magnesian lime- stone with abundant oolites typical of the Noix occur below the fossiliferous Cyrene. Unfortunately no fossils are associated with this oolite, but the relations shown suggest that the Noix is stratigraphically below beds referred to Cyrene. It is not improbable that detailed stratigraphic work in this region will show that both the Noix oolite and the coarsely crystalline lime- stone of Grassy Creek, Pike County, Missouri, and Calhoun County, Illinois, are distinct formations or that the oolite and limestone are one formation, while the Bowling Green and the fossiliferous, earthy, magnesian limestone together constitute another. The sections taken at intervals of 200 yards along Grassy Creek in the western part of sec. 24, T. 54 N., R. 3 W., (Plate VI), show very well the variable character of the lower Silurian. Lithologically the Noix oolite presents several phases. In the bluff south of Louisiana, along Grassy and Noix creeks, and along a branch of Turkey Creek about 1 mile southwest of New "Savage, T. E., Stratigraphy and paleontology of the Alexandrian series in Illinois and Missouri: 111. State Geol. Survey Bull. 23, p. 77, 1917. 26 MISSISSIPPI VALLEY AREA London in Ralls County, it appears as a gray, partly granular limestone with scattered white oolites which make up varying proportions of the mass. Elsewhere along the bluff region of Mississippi Valley, it appears as a dense, chocolate colored, al- most lithographic rock, massive in character and showing a conchoidal fracture. In this rock, the oolites are best seen on the weathered surface as they become lighter in weathering, but even on the fresh surface, the lighter color of the oolites makes them stand out from the darker, almost lithographic ground mass so that in a fresh surface the oolites appear not unlike re- flections in a mirror. The gray-colored oolites of the Noix are distinctive and once seen can never be confused with any other oolite of the Mis- sissippi Valley. They are almost perfectly rounded, and sur- prisingly uniform in size, between 1/16 and 1/32 of an inch in diameter. The thickness of the oolitic beds varies, but in general, the granular, oolitic phase may reach a thickness of 10 feet or more, but the dense phase is commonly in one layer not more than 4 feet thick in most places. The coarsely granular and crystalline phase of the Cyrene is massive in character, light gray or tinted bluish or pink, re- sembling greatly the Burlington limestone in lithologic character. This phase is apparently local in distribution, and may represent erosion remnants of a once more widespread formation, or it may be the undolomitized phase of the Cyrene. The greatest thick- ness observed is about 10 feet. The typical Cyrene as developed in the vicinity of Bowling Green, Edge wood and Cyrene in Pike County and in north- western Lincoln County, Missouri, is brown to blue-gray, earthy, magnesian limestone which weathers into thin beds, but is massive when fresh. It is distinguished from the overlying Bowling Green mainly by its abundant fossils and somewhat more earthy character. The greatest thickness of this horizon is about 20 feet, which was observed in northwestern Lincoln County in the east bluff of Cuivre River south of the road in the NW. J l, sec. 22, T. 51 N., R. 2 W. The Bowling Green dolomite representing the bulk of the Silurian in this region, is well exposed throughout the area of outcrop. It overlies the Cyrene and is a massive, porous dolo- mite, buff to gray when fresh, but weathering to a uniform,' yellowish-brown color. The pores are often stained red with co n 3 ft o o> ^ 05 S a? -o la £5 #vv •••• W ■>*■ K 2 £^|§^3b/4 c s o E 1.5 o c £ < CO 2" C .2 « ? S 2 c p .a 5 o E K STRATIGRAPHY 27 iron and small, dendritic, black markings are common. Fossils are scarce, though imperfect casts formed by the leaching out of fossils are more common. The thickness of the Bowling Green varies greatly from place to place. In the river bluff near Dameron in northeastern Lincoln County, the thickness of Bowling Green is not less than 70 feet; northward from here, the formation though varying greatly in thickness, gradually becomes less and finally pinches out so that it is missing near Louisiana; westward in Pike County, Missouri, the formation also thins, but more gradually, as the westernmost exposures still show from 10 to 20 feet of dolomite. The average thickness for Pike and northern Lincoln counties, Missouri, is between 20 and 30 feet. In Calhoun County, Illinois, the thickness is somewhat more uni- form and averages almost 30 to 35 feet in the southern portion but becomes gradually thinner northward. In Jersey County, Illinois, the thickness is about 40 to 50 feet, but also shows a gradual thinning to the north and a thickening eastward along the southern edge of the county. SEXTON CEEEK LIMESTONE The Sexton Creek limestone which is not so widespread as the underlying Bowling Green formation is best developed in the vicinity of the Mississippi River bluffs (PI. VII, A). In Missouri, it is found along the bluff from south of Dameron in Lincoln County northward to the vicinity of Clarksville, but no exposures of Sexton Creek are found at any distance west of the river in Lincoln, Pike, or Ralls counties. In Illinois good ex- posures are found in both Illinois and Mississippi River bluffs. On the Illinois side of Mississippi River, the Sexton Creek is exposed almost continuously from 2 miles south of Gilead in Calhoun County northward to Rockport in Pike County. Along Illinois River in Calhoun County, the Sexton Creek outcrops as far north as Hardin, and in Jersey County it is exposed in the vicinity of Rosedale. Eastward, however, in the vicinity of Grafton, no exposures of the typical Sexton Creek occur. As commonly developed, the Sexton Creek is a hard, dense, light gray limestone, massive, and found in beds up to 2 feet or more thick. Locally it is almost lithographic or has layers of more coarsely granular rock. In the vicinity of Fleasant Hill, the limestone is interlayered with one or more layers of buff- colored dolomite. Locally, as at Pleasant Hill, the color is mottled red and green, the green color being due to thin irregular 28 MISSISSIPPI VALLEY AREA partings of shaly material which ramify the rock in all directions and cause the beds to weather with irregular and uneven sur- faces. The thickness of the Sexton Creek is extremely variable, ranging from a fraction of a foot to 50 feet, with variations of from 5 to 20 feet found within distances of 100 yards. Such extreme variations in thickness result from erosion channels made previous to the deposition of Sexton Creek which were later filled by the sediments in the advancing Sexton Creek sea. The greatest thickness of rock is found south of Hamburg in Cal- houn County, Illinois, where about 50 feet of Sexton Creek may be seen, but north and south of here the thickness becomes less, so that the average thickness in Illinois is probably less than 15 feet. In Missouri, the greatest thickness is found in the bluffs near the south line of Pike County, and while old erosion chan- nels may show 25 feet or more, the average thickness is not over 10 feet. Devonian System general statement The rocks of the Devonian system in this region consist mainly of limestones with minor amounts of sandstone. The Illinois Geological Survey has been regarding the black Sweet- land Creek shale, which overlies the Devonian limestones as upper- most Devonian, but the Missouri Geological Survey assigns the Grassy Creek shale, which corresponds to the Sweetland Creek shale, to the basal Mississippian for stratigraphic reasons. 13 Although the Sweetland Creek shale may be late Devonian in age, it is much more closely related to the overlying Mississippian than the underlying Devonian in this region, and will therefore be treated with the Lower Mississippian in this report. In Illinois, the Devonian limestones of this area are corre- lated with the Wapsipinicon-Cedar Valley limestones of Iowa. 1416 In northeastern Missouri, the Devonian limestones are separated into four formations as follows: 13 "Branson, E. B., The Devonian of Missouri: Missouri Bur. of Geology and Mines. Vol. XVII, 2nd ser., p. 5, 1923. "Weller, Stuart, Geology of southern Calhoun County: 111. State Geol. Survey Bull. 4, 1907. "Savage, T. E., The Devonian formation of Illinois: Amer. Jour, of Science, 4th Ser., Vol. 49, p. 179, 1920. l|U|l|l|l|l|l|l|i,l,l I'i'i'i'ii 1 |l|>|l|l|l|li!|l|l|l|l J \ l 1 I 11111111- | II II III IIII 1 III- H^^- I lllllllll,! II IIKI III III III III II H ilr-"#M-"-"-"4 1 1 1 1 ; 1 1 1 ] i J " ] 1 1 1 L"_~_"_|iii i---^ § ii^iiiiL" r~_~H I I 'iii'i ill — ~ I'litr- '£ ii'i 1 «' " n ~ "■ 1 1 iii ii lii i| -~-~-i ' ' '1 Jf-'Hrr 11 ! 1 ! 1 ! -~-~-~-~-~ ,|il ,1,1.1,1 l.lili!, — «d — l»il ■ a. — — \| — — c — — III 1 iiiiiii - I -pf | ii H n rH I iii iii ii i i'i '"_«_- °i - -§- - -\~ _-_ *_-_-_ lllllllll - 1 Jl s-f ~ 1 - ~ A- - l\- - ||5 iiiiiii'i- -i-jsf- -I- - -\-ril II 1 iljlil,!,!) 1 )!! - ° ]| lo f- — ° — — -r ~ *j ~ ■p 3 o B r^ 00 STRATIGRAPHY 29 Snyder Creek shale Callaway limestone Mineola limestone Cooper limestone Of these formations, all except the Snyder Creek shale are present in this area. Because of the difference in nomenclature and in the absence of correlations showing the equivalency of the Devonian in Illinois and Missouri, the limestones of this age will be treated as a unit and discussed as the Devonian limestone. DISTRIBUTION Like the exposures of the older rocks, the Devonian outcrops are confined to the flanks of the Cap-au-Gres uplift and were ob- served only in southern Marion, Pike, Ralls, and Lincoln counties, in Missouri, and Calhoun and southwestern Jersey counties in Illinois. Throughout Pike and Lincoln counties, Missouri, and Calhoun and Jersey counties, Illinois, the Devonian reaches a thickness of 20 feet in a few places, and probably averages less than 10 feet. It is patchy in its distribution and is missing en- tirely over wide areas. Thus in the immediate vicinity of Mis- sissippi River valley between Quincy, Illinois, and Clarksville, Missouri, no Devonian is present although the proper horizon is exposed for several miles in both bluffs of the river. In northern Ralls and western Marion counties, Missouri, however, the Devonian thickens rapidly and reaches a maximum thickness of not less than 100 feet in northwestern Ralls County. This increase in thickness of the Devonian in Ralls County is the result of pre-Devonian erosion of lower formations and the subse- quent deposition of Devonian limestones on this slope which marked an early shoreline of the invading Devonian sea. The relation of the Devonian to earlier and later formations is shown in the accompanying generalized sketch (PL VIII). Similar relations hold from north to south as from west to east. The distribution and stratigraphic relations of the Devonian point to a northern, or possibly western, Devonian basin from which the seas transgressed upon the Ozark highland. CHARACTER OF THE ROCK AND STRATIGRAPHIC RELATIONS The best exposures of the Devonian limestones are in Ralls County, Missouri, in the vicinity of Flint Hill church in sec. 28, 30 < MISSISSIPPI VALLEY AREA T. 56 X.. R. 4 W. about three miles northeast of New London, and westward along all the larger tributaries north of Salt River as far west as Shiel in sec. 20, T. 56 X.. R. 6 W. In Marion County. Devonian rocks were observed only in sees. 8. 9 and 22, T. 57 X., R. 7 W., near the junction of Sees Creek and the south fork of North River. The character of these Devonian limestones varies some- what from place to place. In the vicinity of Flint Hill church it rests on either Maquoketa shale or X'oix oolite. Here the basal layer of the Devonian is compact, gray, granular limestone containing pebbles and boulders of Xoix oolite and fragments of chert, and is overlain by about 50 feet of dense, gray to blue, finely crystalline to granular limestone, many layers of which show a brecciated or conglomeratic character on the weathered surface. In the lane back of the house in the east central por- tion of sec. 29. T. 56 X., R. 4 W., sandstone fragments and slabs were observed which apparently came from the lower portion of the formation. Some of the higher limestone layers exhibited intricate cross bedding and a tendency to split into thin layers one inch or less thick. At the east side of the road near the ravine in the south cen- tral part of sec. 24. T. 56 X".. R. 5 W., the Devonian is separated from the Kimmswick by strata less than 20 feet in thickness. This is overlain by several feet of only partially exposed, gray, dense, conglomeratic limestone, upon which lies 8-12 feet of gray sandstone, generally soft and friable but locally cemented into hard, massive sandstone. The grains of the sandstone are well rounded and frosted, not unlike grains of the St. Peter sandstone, but are somewhat smaller. The color of the sandstone is gener- ally gray or yellowish, but locally the weathered surface may be brown. The sandstone is in turn overlain by about 40 feet of dense, line-grained limestone with few or no fossils. About a mile north of the ravine in sec. 24. T. 56 X.. R. 5 W., there is exposed in a road cut above the Devonian limestone about 6 feet of black fissile shale. The limestone beneath the shale is a finely granular, brown dolomite, but farther down the ravine to the east, the dolomite gives way to the dense, gray, brecciated phase. Good exposures of the dense, gray, brecciated limestone with sandstone near the base may also be seen in the ravines in sees. 22 and 23 of T. 56 X., R. 5 W. Along the creek in sec. 28, T. 56 X., R. 6 W., there are also good exposures of the Devonian limestone, but no sandstone member is present in the lower STRATIGRAPHY 31 portion of the section and about 50 feet of dense, massive, some- what brecciated limestone rests on the Kimmswick limestone. Above the dense, brecciated rock, there is a 20-foot layer of mas- sive, somewhat earthy and finely granular, dolomitic rock which is overlain by about 30 feet of more variable limestone in which non-brecciated, dense limestone is interbedded with earthy to granular layers. These upper beds are abundantly fossiliferous in which respect they differ widely from the very slightly fossil- iferous lower portion. Also, the upper 30 feet appears to be separated from the underlying massive layer by an unconformity and the basal layer is locally conglomeratic. The contact of the underlying massive layer and the dense, brecciated limestone is also irregular and it is possible that detailed stratigraphic work will show the Devonian limestone in northern Ralls County to consist of several distinct members or even formations. Along the road north of New London in sec. 13, T. 56 N., R. 5 W., the Devonian limestones are overlain by about 10 feet of black shale which is in turn overlain by the Louisiana lime- stone. The Devonian limestone on the Illinois side of the Mississippi and in Pike and Lincoln counties, Missouri, rests in most places on the Silurian. In the vicinity of the Cap-au-Gres fault in Lincoln County, Missouri, it overlaps the Silurian and rests upon the Maquoketa shales. Northward in the vicinity of Bowling Green and Louisiana in Pike County, the black shale rests on the Silurian and no Devonian limestones are present, so that these Devonian limestones in the Missouri portion of the area exam- ined are limited to a rather small area, including only Lincoln County and southeastern Pike County. Eastward across the Mississippi, the same Devonian lime- stone appears in the bluff of Calhoun County and extends from Llamburg southward to within six miles of the fault. North of Hamburg, the Devonian is missing and the Kinderhook shales rest on the Silurian. On the east side of Calhoun County, the Devonian again appears in Illinois River bluff from Hardin where it dips beneath younger formations southward to the village of Meppen, but south of there the Kinderhook shale rests on Silurian limestones. Eastward across Illinois River the De- vonian again appears in the bluff and is present wherever strata of the proper stratigraphic horizon are exposed, which is from the vicinity of Nutwood to Grafton. 32 MISSISSIPPI VALLEY AREA The Devonian of Illinois and south of Ralls County, Mis- souri, is predominantly a very fossiliferous, earthy, dolomitic limestone, but locally as in the vicinity of Nutwood in Jersey County, and in the bluff in the vicinity of Hardin in Calhoun County, and in Lincoln County, Missouri, it grades upward into a coarsely granular, gray limestone. The dolomitic beds are gray and earthy on the fresh surface, but the weathered face is brown and in the absence of fossils, is distinguished with diffi- culty from the underlying dolomite of the Silurian, where the light gray limestone of the Sexton Creek formation is absent. The basal layers of the Devonian are locally sandy and in some places, as in Calhoun and Jersey counties, thin layers of pure quartzose sandstone carrying the same fossils as the underlying limestone may be found. The thickness of the formation varies from place to place, but the maximum observed in outcrop is less than 20 feet, and near Grafton it is less than 5 feet. Mississippian System lower mississippian sub-system With the exception of small areas of Pennsylvanian rocks and a few scattered remnants of Tertiary gravels, the consolidated rocks exposed in the remaining area are lower Mississippian in age. These Lower Mississippian rocks are separated into sev- eral series which are further subdivided into formations as shown in the following table: Subdivisions of the Lower Mississippian strata Sub- system Group or Series Formation "ft Meramec Ste. Genevieve St. Louis Spergen Warsaw ft 'ta w *«3 W Osage Keokuk Burlington Fern Glen U o Kinderhook Chouteau Hannibal Louisiana Sweetland Creek (Grassy Creek) STRATIGRAPHY 33 K1NDERHOOK SERIES Sweetland Creek (Grassy Creek) shale. — In Missouri north of a line extending east and west through a point several miles south of Louisiana, Pike County, a black, fissile shale containing abun- dant sporangites occurs at the base of the Kinderhook. As observed at most outcrops, the basal portion of the shale is sandy and locally becomes a thin layer of sandstone containing copro- lites and fish teeth. The main bulk of the shale is a massive, thinly laminated shale which is black when fresh, but weathers to a gray or blue gray color. Locally, however, the black fissile character is not developed and the mass of shale is blue-gray. The upper portion is often greenish in color and lacks the finely laminated structure of the black. This shale is well exposed in the river bluff in the vicinity of Louisiana where it rests on the Noix oolite and farther north on the Maquoketa. It is also exposed along Grassy Creek west of Louisiana. In Ralls County, Missouri, exposures are found: (1) in the river bluffs in the vicinity of Saverton; (2) at the road cut in the southern part of sec. 13, T. 56 N., R. 5 W.; (3) where the road crosses a branch of Turkey Creek in sec. 2 about 1 Yi miles south- west of New London; (4) along Cedar Creek in the southern portion of sec. 28, T. 56 N., R. 6 W.; and (5) near the mouth of Brush Creek in sec. 30, T. 55 N., R. 4 W. At the last named lo- cality the black shale is more sandy and contains several well defined layers of sandstone which contain abundant fish remains. Section near mouth of Brush Creek in sec. SO, T. 55 N., R. 4 W. Thickness Ft. In. Limestone, Louisiana 10 — Shale, calcareous — 4 Shale, black laminated 4-5 — Sandstone, fine, gray, soft and friable 3 — Shale, dark, weathers gray 1 3^-2 — Sandstone, conglon eratic (mottled green from included shale). . 1 — Shale, gray, calcareous, massive layer (Maquoketa?) 4 — In Marion County good exposures of the black shale were seen at the ravine in the SW. \i sec. 18, T. 57 N., R. 7 W., also along Sees Creek in sec. 15, T. 57 N., R. 7 W., and in sec. 29, T. 57 N., R. 6 W. The character of the shale in Marion County is similar to that previously described, but the variation in the amount of the black laminated layers is greater. 34 MISSISSIPPI VALLEY AREA Across the Mississippi in Illinois, the black shale is well ex- posed in the river bluffs in the vicinity of Rockport and Atlas in Calhoun County, but becomes thin southward and is not present at and south of Hamburg. Along the Illinois River bluff, the black shale is well exposed just south of Bedford in Pike County, but farther south as near Hardin in Calhoun County where the horizon of the black shale appears, no shale is present and the Louisiana limestone rests directly on Devonian limestone. The black shale is not well developed in Jersey County, but has been observed locally as near the mouth of the ravine where the powder plant is located east of Grafton. The thickness of the black shale is variable. On the Mis- souri side in the vicinity of Louisiana, it is from 4 to 6 feet, along Grassy Creek about 5 to 10 feet, farther north in Ralls County 10 to 20 feet, and in Marion County as much as 40 feet of black shale is revealed. In Illinois similar variations are found. Near Rockport and Atlas, 50 feet or more can be referred to the black shale, though neither the overlying Louisiana limestone or under- lying formations are present. It may be said that the black shale shows increased thickness to the north and east, the greatest increase being toward the center of the Illinois basin. West- ward the formation changes in character and becomes more sandy and grades into sandstone. The relation of the black shale to the underlying forma- tions is distinctly unconformable, for the black shale rests locally on the Maquoketa shale, Silurian or Devonian limestone. The break between the overlying Louisiana limestone and black shale is not so pronounced and no distinct evidence of uncon- formity is observable where both are present. Southward, however, as in southern Calhoun and Jersey counties, Illinois, and in southern Pike County, the Louisiana overlaps the black shale and rests directly on the Devonian (PL IX, A). Louisiana limestone. — The Louisiana limestone is much more local in its distribution than any of the previously described formations. It is best exposed in the Mississippi River bluff between Louisiana and Hannibal, Missouri, where it reaches a thickness of about 60 feet. It continues northwest with only a slight diminution in thickness, but becomes thinner rapidly to the southwest and east. The limestone is well exposed in Marion County in the river bluff at Hannibal and along Sees Creek, Lick Creek and South River in T. 57 N., Rs. 6 and 7 W. It outcrops also in Ralls Illinois State Geological Survey. Bulletin No. 45, Plate IX. A. Unconformable contact between the Devonian and the overlying Louisiana limestone in quarry about 3 miles south of Hardin. Note shaly layer at contact indicated by hammer. B. Contact of Hannibal shale and Chouteau-Burlington limestone near Hardin in Calhoun County, Illinois. STRATIGRAPHY 35 County, but westward from the bluffs it is much thinner, being less than 15 feet thick at its most western outcrops. In Pike County it is prominent in the river bluffs, but becomes thinner rapidly to the west and south, finally disappearing apparently as no exposures have been observed in Lincoln County. Eastward in Illinois the Louisiana is much thinner. In the vicinity of Hamburg in Calhoun County, it is about 5 feet thick and gradually disappears southward. Northward it is present as far as the Pike County line, but no good exposures of Louisiana have been observed any farther north. On the east side of Cal- houn County, an 8-foot outcrop of Louisiana appears in the bluff just north of Hardin, and continues southward with a gradual decrease in thickness until it pinches out entirely about 4 miles south. The Louisiana limestone does not appear again north of Hardin though its horizon is exposed near the north line of the county and south of Bedford in Pike County. Across Illinois River in Jersey County, several feet of Louisiana lime- stone are exposed in the vicinity of Nutwood, but it does not appear in the bluffs near Grafton. Where best developed, the Louisiana is a dense, practically lithographic limestone occurring in 2 to 6-inch layers separated by thin partings of shale. The rock weathers light gray and the average bluff exposure resembles greatly a wall of masonry. The fracture is conchoidal and the rock gives forth a ringing sound when struck with the hammer. Locally, however, the upper beds may be dolomitic and the rock then takes on a buff or brown, sandy appearance. Elsewhere, thin layers of brown dolomite alternate with gray limestone layers causing the bluff exposures to appear banded. Where the upper portion is pre- dominantly dolomitic it often contains numerous calcite geodes varying in size from less than an inch to several inches in diam- eter. In general, the variations in the character of* the rock are confined to the upper half of the formation and the lower portion is very similar throughout the region of outcrop. At most exposures there is found below the limestone non-laminated, massive, blue-gray shale which reaches a thickness of several feet near Louisiana, but at most exposures may be less than a foot. Hannibal shale. — In the vicinity of Hannibal, Missouri, the Louisiana limestone is overlain by about 60 feet of greenish, sandy and generally non-laminated shale. Near Hannibal and to the north and west in Marion and Ralls counties, the shale is predominantly sandy in the upper portion, and was termed "Ver- 36 MISSISSIPPI VALLEY AREA micular Sandstone" by the older geologists because of its sandy character and the presence of small, ramifying, tubular holes filled with softer, earthy material than the surrounding mass. Such holes are considered to be worm borings. Southward as in southern Pike and Lincoln counties, Missouri, the shale becomes less sandy and thinner, so that in Lincoln County, the shale is only about 40 feet thick and locally less. Still farther south in Missouri along Missouri River, just west of Hamburg in St. Charles County, the horizon of the Hannibal shale shows the overlying Chouteau resting on 6 feet of pure, medium-grained, massive sandstone, which is, in turn, underlain by about A 1 /^ feet of gray, sandy, fossiliferous oolite. At Grafton in Jersey County, Illinois, about 1 foot of fossiliferous, sandy oolite occurs at the base of the Hannibal, and farther north at Hamburg in Calhoun County, the base of the Hannibal shale consists of dense, siliceous limestone interbedded with sandy shale. At this hori- zon, fossiliferous oolite called "Hamburg oolite," the fauna of which is described by Weller 15 , is intercalated locally with the siliceous limestones and shales. Fossiliferous, oolitic limestone has been noted at this horizon on the east side of Calhoun County in the road cut along the bluff just south of Cliffdale. Farther north in Pike County, Illinois, there is exposed in the creek bed in the NW. K, sec. 25, T. 6 S., R. 5 W., about 1 mile southwest of Rockport, 6 feet of massive, oolitic conglomerate consisting of pebbles of lithographic Louisiana limestones in a matrix of oolites. The main body of the Hannibal shales in Illinois, as in Missouri, is thinnest to the south and becomes gradually thicker northward. Thus near Grafton in Jersey County and in south- ern Calhoun County it is between 30 and 40 feet, but near the north line of Calhoun, is between 80 and 100 feet, this interval continuing into Pike County where the Hannibal shale rests on the Sweetland Creek so that the contact is not everywhere ob- servable. The character of the shale likewise changes from south to north. In the southern portion, the shale is mostly non- laminar with a structure like earthy cement rock. Farther north it becomes increasingly siliceous; in northern Pike County, Illinois, the upper portion is a massive calcareous fine-grained sandstone, in places abundantly fossiliferous capped by from 1 to 15 feet of dense, siliceous limestone in the vicinity of Kinder- i»Weller, Stuart, Trans. St. Louis Acad. Scl., vol. 16. No. 7, p. 465. STRATIGRAPHY 37 hook and northward. The limestone shows a gradual thicken- ing north from Kinderhook and at Fall Creek about 10 feet of sandy dolomite, lithologically similar to that below the limestone occurs above the limestone. At these northernmost exposures, the Hannibal shale is immediately overlain by Burlington limestone (PI. IX, B) which is locally conglomeratic at the base with pebbles of the siliceous limestone in a matrix of the coarsely granular limestone. Chouteau limestone. — In the southern portion of the area in southern Pike, Lincoln and St. Charles counties, Missouri, and in Calhoun and Jersey counties, Illinois, the Hannibal shales are overlain by a limestone which is referred to as the Chouteau. The limestone is somewhat variable in character, but in most exposures appears as a dense, tough and somewhat earthy limestone with a few scattered chert nodules. The weathered surface becomes gray in color and is often characterized by a knotty appearance brought about by softer, shaly portions weathering away from more resistant cores. The more shaly layers have a speckled appearance, caused by scattered faces of crystalline calcite in a dense drab background. Small calcite geodes, seldom more than an inch in diameter, are prominent in the soft, earthy and dolomitic phase. Locally, as in south- ern Calhoun County, the basal layer may be granular and in Jersey County, the topmost beds are, in places, lithographic in texture. The Chouteau is well exposed in Missouri River bluffs east of Hamburg in St. Charles County, and in Lincoln County, Missouri; in Illinois in the river bluffs of Calhoun County in the vicinity of Hardin, and in bluffs of southwestern Jersey County. The limestone in Lincoln County, Missouri, southern Calhoun and Jersey counties, Illinois, is from 40 to 60 feet thick, but thins northward gradually to Calhoun County, Illinois, and Pike County, Missouri, north of which it disappears. The Chouteau appears to be conformable with the underlying shale and the interval occupied by both remains practically con- stant, because as the limestone thins northward the shale in- creases in thickness. In Calhoun and Pike counties, Illinois, the approximate contact of the overlying Osage group and the Chouteau is marked by a soft, dolomitic layer which in the bluff face is usuallv weathered back several feet. 38 MISSISSIPPI VALLEY AREA OSAGE SERIES The Osage series, consisting mainly of crinoidal limestones with only minor amounts of shale, is best exposed in the bluffs along Mississippi and Illinois rivers, and in western Ralls, Pike and Lincoln "counties and central St. Charles county, Missouri. The divisions are given in the table, page 32. Fern Glen formation. — The Fern Glen formation has been recognized only in the vicinity of Chautauqua and Grafton in Jersey County, Illinois, but the red and green shales and shaly limestones which form so conspicuous a feature of the formation at its type locality are almost wholly lacking. At Chautauqua a 25 to 30-foot massive layer of granular limestone free from chert is found above the dense limestone of the Chouteau and is overlain by about 25 feet of shaly limestone, predominantly greenish in color but locally pink or red, containing thin layers or nodules of blue or green chert. Above this shaly limestone lies the white, coarsely granular, crinoidal limestone of the typical Burlington. A somewhat similar section occurs at Graf- ton, but the shaly phase is even less pronounced, the shale being limited to thin partings between layers of granular limestone. This formation is undoubtedly present in St. Charles and Lin- coln counties, Missouri, but the horizon was not examined in those counties. Undoubtedly the Fern Glen continues north- ward from Grafton, but assumes more and more the character of the Burlington, and can be distinguished only by its fossils. Like the Chouteau, it thins to the northward and is certainly not present far north of Kinderhook. Burlington-Keokuk limestone. — Above the Fern Glen, coarse- ly granular, crinoidal limestone of the Burlington-Keokuk occurs in great thickness. In the northern part of the area this mass of limestone is readily divisible into two formations on the basis of the fossils and lithology, but in the southern part there is no apparent break, and while both formations are present, it is practically impossible to find a line of separation. The Burlington-Keokuk limestone is well exposed along the bluffs on the Illinois side from east of Grafton northward to Dallas in Hancock county and also outcrops along most of the creeks in southern Pike and Calhoun counties. In Missouri, it shows in the bluff from Kissinger, Pike County, northward to the north line of the State and is exposed along most of the creeks STRATIGRAPHY 39 in central St. Charles and in western Lincoln (PI. X, A), Pike, Ralls, and Marion counties. The Burlington limestone is typically a massive, coarsely granular, light gray, crinoidal limestone. Bedding planes are usually indistinct in fresh exposures, but where weathered, the rock shows beds of 6 inches to 8 feet thick. The details of the section vary from place to place, and locally there are inter- calated with the gray limestone varying amounts of brown, dolomitic rock. Chert, abundant especially in the upper por- tion, occurs as irregular layers and nodules which may be thin plates or masses a foot or more thick. The thickness of the Burlington, including the cherty transition beds, is about 100 feet. The total thickness of the Osage, therefore, is about 160 feet in the northern portion and between 250 and 300 feet in Jersey County, but the increase to the south is due mainly to the presence of the Fern Glen formation, the Burlington-Keokuk itself remaining fairly con- stant. In the northern part of the region where the Keokuk is recognized as a distinct formation, it consists of layers of rather coarsely granular limestone 6 inches to 6 feet thick, separated by shaly layers up to two feet thick. The texture, while granu- lar, is finer than the Burlington, and less crinoidal, and the color is usually a bluish-gray as compared with the light gray or white color of the Burlington. Chert, as thin platy layers and nodules, is abundant near the top of the formation, and again at the base where an interval of about 30 feet of very cherty limestone marks the transition of the Keokuk into the Burlington. The large, middle portion of the formation, however, is relatively free from chert. Southward, the shale intervals become progressively smaller and the limestones more crinoidal and more coarsely grained until it becomes difficult to distinguish the two. The thickness of the Keokuk exclusive of the lower 30 feet of cherty limestone is between 60 and 80 feet, an interval surprisingly constant for Clark and Lewis counties, Missouri, and Hancock County, Illinois. MERAMEC SERIES The Meramec series, which is divided into several formations as shown in the table (page 32), outcrops in the vicinity of the Mississippi River bluffs, in Lewis, Clark, southern Lincoln and 40 MISSISSIPPI VALLEY AREA St. Charles counties, Missouri, and in Hancock, Adams, northern Pike and Jersey counties, Illinois, and though it outcrops mainly in the vicinity of the river bluffs it underlies most of the counties mentioned. In this preliminary study no break was observed between the Meramec and Osage series in this area, nor was any con- vincing evidence found of a break between the different forma- tions of the Meramec series. Warsaw-Spergen formations. — The Warsaw and Spergen are recognized as distinct formations over most of the area, but it is extremely difficult, if not impossible, at most localities to say where one begins and the other ends. In the northern part of the region these formations are dominantly shale with only minor amounts ' of limestone, except locally, but in the southern part they become increasingly calcareous con- sisting mainly of limestone in the upper portion, but retaining the shaly phase in the lower portion. This horizon is probably the most variable in the whole Lower Mississippian section, and no two sections taken more than half a mile apart show much agreement in lithologic details. East of Niota in the NE. %, sec. 17, T. 7 N., R. 7 W., in northern Hancock County, an old abandoned quarry exposes a vertical face 50 to 60 feet high, which at the top shows about 10 feet of cross-bedded, gray limestone that splits readily into thin layers along the planes of the cross-bedding. Below this cross- bedded limestone is about 40 feet of massive, porous, brown dolomite* consisting mainly of Bryozoa, and occurring in layers up to several feet thick. A short distance down stream the granular, cherty limestone of the Keokuk is found at an ele- vation not more than 20 feet below the dolomite of the quarry. In the region west of here as shown at the abandoned quarry near the center of sec. 11, T. 7 N., R. 8 W., there occurs below the St. Louis a 3 to 4-foot layer of dolomite containing many small, scattered quartz grains about the size of a pin head. This is underlain by 3 to 5 feet of bluish, calcareous shale, below which is a 20-foot ledge of finely crystalline dolomite consisting mainly of Bryozoan fragments, and this ledge is in turn underlain by shale. At Warsaw (PI. X, B) the following section occurs: Illinojs State Geological Survey. Bulletin No. 45, Plate X. A. Structural slope of steeply dipping Burlington-Chouteau limestone on the west limb of the Lincoln fold about 3 miles northeast of Silex. The strike of the rocks is N. 15°W. and the dip 65°W., Lincoln County, Missouri. B. Lower Warsaw geode bed near Warsaw, Hancock County, Illinois. Illinois State Geological Survey. Bulletin No. 45, Plate XL A. Possible contact between Ste. Genevieve and underlying St. Louis limestone in an old quarry northeast of Spanish Lake, Missouri. B. Tilted St. Louis imestone on the south limb of Lii Grafton, Jersey County, Illinois >ln fold. 6 miles viresl of STRATIGRAPHY 41 Section immediately below the St. Louis limestone at Warsaw, Illinois Thickness Feet Dolomite, dense, earthy with scattered quartz grains 1-2 Limestone, gray, granular, distinctly cross-bedded 2-3 Shale and limestone, earthy, magnesian 2-3 Shale with lenses of blue-gray more coarsely granular fossiliferous limestone Shale, calcareous with numerous geodes in lower portion 35 Below the St. Louis, in the ravine east of the north-south road in the southeast corner of the SW. \i, sec. 34, T. 4 N., R. 9 W., 48 feet of lenticular, earthy, magnesian limestone grading to shale may be found. None of the granular limestone lenses found farther north are present in the 60 feet exposed here. Such partial sections of this horizon as are exposed along the creeks of Adams and northern Pike counties show rocks similar to those already described, with the exception that the earthy, magnesian limestones and shales predominate. Farther south in Jersey County, the upper portion contains larger amounts of granular limestone and only the lower 30 to 40 feet are shale. Locally, oolitic layers are interbedded with the granular lime- stone. In Missouri, where this horizon is well exposed in the vicinity of the bluffs in Clark and Lewis counties, it shows characteristics similar to those on the Illinois side. A good exposure of the horizon is to be seen along the ravine just north of St. Francis- ville in sec. 32, T. 65 N., R. 6 W. Other good exposures are to be seen along the bluff northward to Canton in Lewis County. In St. Charles County, the Warsaw-Spergen is well exposed in the bluff of Missouri River north of Greens Bottom, sec. 28, T. 46 N., R. 4 E., but here the upper beds are more calcareous and shale predominates only in the lower 40 feet. The thickness of this group increases from north to south. In the northern portion as in Hancock County, Illinois, and Clark County, Missouri, the thickness is between 60 and 80 feet, while in St. Charles County, Missouri, it is between 125 and 150 feet, and attains a similar thickness where exposed in Jersey County. St. Louis and Ste. Genevieve formations. — Unlike the pre- ceding group the St. Louis and Ste. Genevieve are mainly lime- stones (PL XI, A) and contain practically no shale, except thin partings. 42 MISSISSIPPI VALLEY AREA The distribution of these formations is practically the same as that of the Warsaw-Spergen, and at most exposures St. Louis limestone is found capping the lower formation. In the more northern localities as in Adams and Hancock counties, Illinois, and Lewis and Clark counties, Missouri, the basal portion of the St. Louis is a brecciated or conglomeratic limestone from 10 to 30 feet in thickness. Throughout this region the base of the formation consists of a more or less nodular layer 2 to 3 feet thick, of dense, hard, very finely crystalline limestone, characterized by small crenulations which are made prominent by thin lines of a darker substance at intervals of about Y± of an inch. Immediately above this basal layer, the formation consists of boulders of limestone in a matrix of shale which is locally sandy and farther south becomes limestone. The limestone boulders are usually light gray, dense, similar in character to the overlying layers but different from the under- lying formations. The boulders vary in size from less than 3 inches to several feet in diameter. This horizon becomes less conspicuous to the south and at the southernmost exposures of the St. Louis in St. Charles and Lincoln counties, Missouri, and Jersey and Madison counties, Illinois, it is not evident near the base of the formation. Above the brecciated or conglomeratic beds, the limestone is commonly a light gray, hard, dense limestone, almost lithographic in texture, and characterized by conchoidal fracture. Generally it occurs in layers of from a few inches to two feet thick, which are separated in places by partings of light green, calcareous shale. Locally, layers of brown dolomite and even sand lenses are found not far above the brecciated portion. Chert layers and nodules are common. In Lewis and Clark counties, Missouri, where this formation may be from 40 to 60 feet thick, the upper portion contains oolitic layers interbedded with the dense, and at several localities a sandstone layer up to 6 feet thick is present. At the more southern localities, as in the vicinity of Alton and the southern tip of Calhoun County in Illinois, and eastern St. Charles and southern Lincoln counties, Missouri, the St. Louis limestone is much thicker, but the light gray color and the dense texture are also characteristic here. Oolitic beds are rare, although not unknown in this formation, and do not be- come prominent below the Ste. Genevieve. The lower portion of the St. Louis contains more or less magnesian limestone. STRATIGRAPHY 43 The crenulated layer so characteristic of the base of the St. Louis in the northern part, is not evident in the southern part, nor is the brecciated horizon developed near the base. However, near Alton and in the bluffs of southern Calhoun County, Il- linois, and in southern Lincoln County, Missouri, a well defined brecciated zone made up of limestone boulders of different kinds of St. Louis limestone cemented together by limestone occurs about 120 feet above the base of the St. Louis, and curiously enough the layer of limestone below it shows the crenulated character so typical of the basal St. Louis farther north. The topmost beds exposed in the bluff near the town of Alton are re- ferred to the Ste. Genevieve limestone. These upper beds include at their base a massive layer 15 to 20 feet thick of oolitic limestone, overlain by about 18 feet of massive sandstone, above which is more oolitic and lithographic limestone. The oolitic limestone of Lewis, Clark and St. Louis counties, Missouri, should also be referred to the Ste. Genevieve, but until more detailed work is done in this area the exact relations of the St. Louis and Ste. Genevieve in this area will remain in doubt. The thickness of the St. Louis and Ste. Genevieve is very variable. In the more northern localities this horizon is overlain by the Pennsylvanian and was deeply eroded before the deposi- tion of that period. As a result, there are great differences in thickness within short distances; locally all the St. Louis has been removed and the Pennsylvanian rests on older formations. In general, however, the thickness in Clark and Lewis counties, Missouri, and Hancock and Adams counties, Illinois, ranges between almost nothing and 60 feet. To the south there is a gradual thickening of this formation and in the vicinity of Alton, it reaches a thickness between 250 and 270 feet, of which 200 to 225 feet are St. Louis'. Pennsylvanian System Rocks of the Pennsylvanian system are present locally within the area, but are not distributed widely enough to be of service in determining the structure., As observed, they consist mainly of shales and sandstone with minor amounts of limestone. They occur as scattered outliers in eastern St. Charles, southern Lincoln, northern and western Marion counties, and probably are present beneath the drift over most of Lewis and Clark counties. In Illinois they 44 MISSISSIPPI VALLEY AREA were observed only in the eastern part of Hancock County, cen- tral and eastern Adams County, northern Pike County and the southern end of Calhoun County. Tertiary System In southern Calhoun County, one or two of the ravines revealed bronzed and polished chert pebbles, typical of gravels in southern Illinois and Missouri, considered as Tertiary in age, and it is probable that small patches of such deposits exist beneath the overlying soil and drift at other localities within this area. Quaternary System Deposits of gravel, till and loess cover most of the upland back from the bluffs in much of the northern area, so that rock outcrops are limited to the vicinity of the bluffs and the larger streams. In the more southern area of Calhoun County, Illinois, and St. Charles, Lincoln, Pike, Ralls and Marion counties, Mis- souri, however, the drift is thin or wanting, and outcrops are abundant. CHAPTER III— STRUCTURE General Statement The structure shown on the structure map (PL I) is based on the elevation of the base of the Burlington limestone. This contact was chosen because it was observed at the greatest number of places; is easily recognized in well logs; is essentially parallel to the underlying formations in small areas; and the intervals separating it from other formations in the geologic column above the St. Peter sandstone are fairly well known. A fifty-foot contour interval is used in representing the struc- ture, as it is felt that this is the smallest interval that could be chosen and still be consistent with the methods used and amount of data available. Most of the elevations upon which the structure is based are given in Table 1, page 8. Since the scarcity or abundance of outcrops has a direct bearing on the accuracy of the detailed structural work, the plotted outcrops suggest the areas in which such work is feasible and also shows regions in which structural details will have to be obtained from subsurface data. It should be remembered in using the map, that the correct- ness of any contour is dependent upon the number of observa- tions upon which it is based. Therefore, in areas where outcrops shown are few or entirely lacking, the structure represents the writer's opinion only. The structural mapping of such areas is subject to change as more data become available. It is advisable in all cases that detailed structural work be done before any drilling is undertaken. Structural Features The most pronounced structural feature of the region is a large anticlinal fold which extends from Grafton in Jersey County, Illinois, westward across southern Calhoun County, thence across the Mississippi Valley, and continues westward and southwestward across Lincoln, Pike, Ralls, and southern Marion counties, Missouri. For convenient reference, this fold will be known as the Lincoln anticline, because it reaches its greatest development in Lincoln County, Missouri. (45) » 46 MISSISSIPPI VALLEY AREA Associated with this fold is a large fault designated by older writers of geology as the Cap-au-Gres fault. This fault parallels the Lincoln fold and breaks it just south of the crest. In south- western Jersey and southern Calhoun counties, Illinois, and in Lincoln County, Missouri, the fold is most pronounced and ap- parently dies out both to the east and west. The next fold of regional importance is the anticline referred to as the Pittsfield-Hadley anticline in the Illinois State Survey reports 16 . This fold attains its greatest prominence near Pitts- field in Pike County, Illinois, but can be traced from Bedford, Illinois, to LaGrange, Missouri. In the vicinity of Quincy, it flattens out into a broad, flat, terrace-like structure, which is probably caused by the convergence of three distinct anticlinal areas. The general trend of this terrace, which is a prominent structural feature throughout western Adams County, Illinois, is about north and south. The remaining area, which is practically flat, shows some structural features, but these are more or less local. South of the Cap-au-Gres fault a pronounced syncline, the axis of which has an east-west direction, extends from the vicinity of Troy, Missouri, to Brussels, Illinois. LINCOLN FOLD The Lincoln fold is not a simple symmetrical fold, but is rather an area of uplift on which are many minor structural features such as anticlines, domes, synclines and faults. Direct evidence of the Lincoln fold and associated fault is first seen in Illinois about one mile east of Grafton in the ravine in the NW. J£ of sec. 14, T. 6 N., R. 12 W., where the powder plant is located. The bluff east of the ravine is capped by Bur- lington limestone, while west of the ravine Silurian limestone makes up the bluff. In the ravine itself the rocks are tilted and strongly suggest faulting, though the displacement here is not very great, certainly less than fifty feet. In the town of Grafton west of the road leading north in the NW. \i of sec. 15, T. 6 N., R. 12 W., the Silurian limestone along the bluff dips locally 3 to 4 degrees south, showing the pres- ence of an anticline parallel to the bluff. The westward rise of the rocks indicate it to be an eastward pitching structure. "Coryell. H. N., Parts of Pike and Adams counties: 111. State Geol. Survey Bull. 40, p. 75, 1919. Illinois State Geological Survey. Bulletin No. 45, Plate XII. Oolitic limestone 'i'i' i V Limeslone Dolomite Shale Cross sections to show the relation of the Cap-au-gres fault to the Lincoln fold. A. Along Illinois River bluff, Jersey County, Illinois. B. Along Illinois River bluff, Calhoun County, Illinois. C. Along Mississippi River bluff, Calhoun County, Illinois. D. Along Mississippi River bluff, Lincoln County, Missouri. STRUCTURE 47 Farther west along the bluff road, in sees. 13 and 14, expo- sures of St. Louis limestone and Pennsylvanian shale are seen dipping steeply to the south (PL XI, B), and still farther west the cross section of the fold as seen along the north-south road in sec. 9, T. 6 N., R. 13 W., shows an unbroken arch having a gentle slope of about twenty-five feet per mile to the north and a steep dip of almost forty-five degrees to the south. The lowest formation exposed is the Kimmswick limestone. Across Illinois River, the fold again appears in the bluffs in sec. 35, T. 12 S., R. 2 W. Although the south limb still re- tains its steep dip, the north limb is undulating with a dip of about 25 feet per mile, and the crest of the fold, located about three miles north of where the sharp change in direction of* dip occurs (PL XII, A), is approximately sixty feet higher than near the bend, but is about fifty feet lower than in Jersey County. As no continuous section showing the change from the steeply dipping south limb to the gently undulating north limb can be seen here, it is possible that there is a break or slight fault in the fold. The crest of the fold rises sharply to the west and in the Mississippi bluffs in sec. 29, T. 12 S., R. 2 W., if the original structure were restored would be about 350 feet higher than on the Illinois side of Calhoun County (PL XII, B). The forma- tions of the south limb are almost vertical, and even the north limb has a pronounced dip. Furthermore, the abrupt change in dip on the south limb is marked by actual displacement which causes Maquoketa shale to abut against St. Peter sandstone, making a throw of about 300 feet (PL XII, C). In Missouri, exposures in the river bluff about a mile north of Winfield show the crest of the fold to have been about 100 feet higher than in Calhoun County. The south limb is faulted and the formations immediately adjoining the fault are prac- tically vertical. The displacement of the fault is still about 300 feet, but the formations brought into contact are the Jefferson City dolomite and the Plattin limestone (PL XII, D). The north limb of the fold retains its more gentle dip. The bluff section north of Winfield apparently marks the approximate top of a dome, for westward the crest of the anti- cline becomes lower and in the southeast corner of T. 50 N., R. 1 E. is about 200 feet lower than in the bluff. West from here it rises again, and in the northwest corner of T. 50 N., R. 1 E., reaches about the same elevation as near the bluff. The trend 48 MISSISSIPPI VALLEY AREA of the fold which up to this point has been about N. 70° W. changes somewhat abruptly and becomes almost due north, veering only slightly to the west. This sharp northward bend of the fold is apparently accompanied by faulting, for highly disturbed beds were observed in sec. 3, T. 50 N., R. 1 W., and also along the road just north of sec. 3 in the adjoining township. The strike of the rock in the former case is N. 20° W. and the dip 55 degrees west, while in the latter case the strike is about north and south and strata almost vertical. The northward trend of the axis is of short extent, for in the northwest portion of T. 51 N., R. 1 W., the axis turns westward again and crosses the northern part of T. 51 N., R. 2 W., in a general east-west direction, and shows a gentle plunge to the west. Near the west line of the township it changes direction again to northward, crossing Pike County in a N. 20° W. direc- tion, and continuing into Ralls County almost to New London where it again turns to the west and passes into and crosses Marion County in a N. 50° W. direction. The faulting which is so intimately associated with the folding throughout most of Lincoln County, Missouri, and Cal- houn County, Illinois, is not prominent west of the northward bend of the fold, the only evidence of faulting west of here being the faulted zone along the creek in sec. 4, T. 51 N., R. 3 W. For a distance of several hundred yards to the east of the road, the rocks are greatly fractured and minor faults extend in every direction. It is possible, however, that this faulted zone repre- sents a continuation of the main fault, though the total dis- placement along the faulted zone does not appear to be more than fifty feet. Just south of New London, the trend of the fold becomes more westerly again — N. 70° W., and retains this direction as far west as Spaulding near the southeast corner of T. 56 N., R. 6 W. Throughout this extent the south limb is steeply folded, but the north limb dips gradually. In the vicinity of Spaulding, beds have been observed dipping so steeply as to suggest local fault- ing. Beyond Spaulding, the rocks take on a more northerly trend once more, and the fold crosses Marion County in an ap- proximate N. 45° W. direction with the folding less and less pro- nounced. o o 6 o o o o o m CO r^ CO STRUCTURE 49 THE PITTSFIELD-HADLEY ANTICLINE The Pittsfield-Hadley anticline, which is roughly parallel to the Lincoln fold, lies well down the north slope of that struc- ture. Its easternmost expression in the area under discussion is found in the Illinois River bluff near Bedford in T. 6 S., R. 2 W., where the base of the Burlington limestone at the crest of the fold is about 150 feet higher than the same horizon at the foot of the south limb. From this point, the fold has a general northwest trend, crossing Pike and southeastern Adams counties, Illinois, entering Missouri near the town of LaGrange in T. 61 N., R. 6 W., and continuing across Lewis County. The crest of the fold rises gradually west of Bedford to the top of the elongated dome located near the center of T. 5 S., R. 4 W., Pike County, where it begins to descend, continuing with possible minor interruptions throughout its extent. The amount of closure represented in the dome is about 175 feet. WESTERN ADAMS COUNTY TERRACE Near the center of T. 3 S., R. 7 W., Adams County, the Pittsfield-Hadley anticline, which crosses Pike County as a simple fold, broadens out and diverges into three distinct axes. One axis retains the original trend and crosses over into Missouri near LaGrange, as mentioned before. A second one trends a little west of north to near the center of T. 2 N., R. 9 W., where it changes to a northwesterly direction, entering Missouri about half way between Gregory and Canton and continuing across northeastern Lewis County and southwestern Clark County. The third axis strikes northward through the tier of townships included in R. 7 W. as far as T. 2 N., where it takes on a more easterly direction and apparently dies out. East of this axis, the rocks dip gradually to the east, and west of the LaGrange axis the rocks dip to the west, but in the intervening area the strata are practically flat although they, dip gradually to the north. THE SOUTHERN LINCOLN COUNTY SYNCLINE South of the Cap-au-Gres fault the rocks are folded in a large eastward plunging syncline, the axis of which extends from immediately north of Brussels in southern Calhoun County west across southern Lincoln County, Missouri, beyond the 4 50 MISSISSIPPI VALLEY AREA town of Troy in T. 49 N., R. 1 W. The south limb of the syn- cline strikes almost due west in western Lincoln County, but in St. Charles County it is northwest-southeast. MINOR STRUCTURES Within the area included by Hancock County, Illinois, and Lewis County, Missouri, the rocks are comparatively flat lying and do not present variations of over 100 feet. Such irregulari- ties as do occur are more or less local, but a few structurally high areas appear to have regional significance. In Lewis County, Missouri, the rocks are arranged in a series of low, broad folds having a distinct northwest-southeast trend and as seen in the river bluffs, the northern third represents the south limb of an anticline whose crest is north of the State line. The middle third shows a low arch and the southern third represents the south limb of an anticline whose axis lies south of the County line. A reflection of the broad central fold is seen in Hancock County, Illinois, in the structurally high area which extends from north of Warsaw eastward across the county past Carthage and leaves the county near the junction of Tps. 5 and 6 N. Other structurally high areas are found near Nauvoo in the northwest corner of T. 6 N., R. 8 W., the center of T. 7 N., R. 8 W., and the north half of T. 7 N., Rs. 5, 6 and 7 W. A high area is also indicated in the western part of T. 4 N., R. 5 W. In addition to minor folds mentioned, many smaller folds are indicated in the structure sections of the bluffs and a small fold is also shown in the Missouri River bluff west of the center of T. 46 N., R. 4 E. Periods of Deformation The structure as represented on the structure map is for the most part the result of post-Pennsylvanian deformation, but inasmuch as it is based entirely on data obtained from Missis- sippian rocks it is not improbable that it diverges somewhat from a representation of only Pennsylvania deformation, and com- bines elements of both post-Pennsylvanian and pre-Pennsyl- vanian deformation. A study of the stratigraphy shows that the rocks were ele- vated and submerged several times within the geologic history of the region, and that the changes in level were sometimes "ac- STRUCTURE 51 companied by warping. Since no oil has ever been found in rocks older than the Kimmswick ("Trenton"), a consideration of deformation previous to that time is not pertinent to a discus- sion which deals with a structural reconnaissance made for the purpose of considering the relation of structure to the possibility of finding oil, and will therefore not be included. Times of submergence were usually inaugurated by a warp- ing and sinking of the areas adjoining the Ozark region, while the Ozarks themselves apparently remained stationary or sank more slowly. Upon emergence the Ozark region was generally the first to become land, and since the Ozark region was land during most of Paleozoic times the formations laid down during that time thin out towards the Ozarks and often change in char- acter as the old land masses are approached. The retreat of the sea after the Kimmswick limestone had been lain down was accompanied by a slight tilting of the strata to the southeast, and possibly a slight downwarp of the beds just north of the area included in this report. Subsequent erosion, therefore, left deposits which thicken to the south and east, the rate of increase averaging not much over two feet per mile, al- though there is local variation. During the next submergence or possibly during the emer- gence after the Maquoketa shale had been deposited, the surface was again tilted, but this time to the north, for that formation thickens to the north and east. The amount of tilting was again small in the northern portion of the area, but becomes increas- ingly greater to the east where the dip may reach as much as 20 feet or more per mile. During the ensuing Silurian period, and possibly immedi- ately after, there may have been a slight sagging in the southern portion of the area, as evidenced by the presence of Silurian strata in Jersey and Calhoun counties, Illinois, and in northern Lincoln, Pike, and southern Ralls counties, Missouri, and the absence of these formations in the north central part of the area. They are also known to be present in the eastern portion of the area, although in diminished thickness, but their very presence there suggests continued slight tilting to the east. The presence of the Silurian in the southern portion of the area may also be accounted for by considering that the area was lowered more than the rest by erosion and by subsidence subsequently became occupied by an arm of the Silurian sea. 52 MISSISSIPPI VALLEY AREA North of the area under consideration there is known to have been pronounced sagging during Silurian times. Though the Devonian in Illinois and eastern Missouri was marked first by depression to the southeast, south of the region studied, and later by depression to the north of the area studied, the amount of folding or warping which actually took place within this area is apparently negligible, and although a thick- ness of 125 feet and more of northern Devonian rocks does oc^ cur in Ralls County, their relations are such as to suggest that they are deposits formed in bays occupying pre-Devonian erosional lowlands. If the black shale above the Devonian limestones is con- sidered Mississippian in age, then the Mississippian was inau- gurated in this area by a tilting to the northeast. As in earlier periods the amount of tilting is appreciable only if widely sepa- rated areas be considered, as its average is less than 5 feet per mile, though it varies locally. In the transition from Mississippian to Pennsylvanian times there was warping as is shown by the fact that apparently flat lying Pennsylvanian rocks rest at the same elevation on rocks as low as the Burlington, or as high as the St. Louis strati- graphically. The amount of warping or tilting is slight and ap- pears to correspond roughly with existing structures. Besides the main epochs of warping mentioned there have been many others whose records are not readily discernible, and it is impossible with the data at hand to attempt to outline even the larger features. The resulting effect of these different periods of warping has been to destroy the parallelism of the formations of different periods, or even formations of the same period. Apparently, however, the last period of warping was the greatest, and since all deformation of surface rocks is reflected to some depth in the underlying strata, structures corresponding to the surface rock structure are also found in the underlying beds. It is possible, however, that the outlines of low, broad folds found at the surface may be completely neutralized in the lower strata by underlying structures formed at some earlier period, and it is just as possible that folds which are present in lower rocks do not have any surface expression and can be discovered only from study of subsurface data. Difference in trend of early folds crossed by later folds tends to alter outlines of the struc- ture, but in this area later folds appear to parallel and accentuate earlier ones. o o o o o o o o o o o o o o o o o o O o o o o o C\J CO ■*!- to u r^ co O o C\J CO STRUCTURE 53 In this region, the major effect has been to cause a gradual divergence of the strata toward the center of the Illinois basin to the east. Plates XIII and XIV illustrate the changes from north to south on the Missouri and Illinois sides of the Mississippi Valley area. Plate XV represents a generalized section from Clark County, Missouri, to Hancock County, Illinois; Plate XVI represents one farther south across Marion County, Missouri, and Adams County, Illinois, and Plate XVII one across Pike County, Missouri, Calhoun and Western Greene counties, Illinois. Many other local and minor variations also occur, but these can be determined only from a detailed study of the area. CHAPTER IV— OIL POSSIBILITIES Introduction Except for the small amounts of gas obtained from the Pittsfield-Hadley dome in Pike County, Illinois, there is no pro- duction of oil or gas within the area described in this report. The nearest producing field is the Colmar field, located near the eastern edge of Hancock County, Illinois, in T. 4 N., R. 4 W., in which the oil is obtained from discontinuous sand lenses at the top of the Maquoketa shale. South of the area there is oil production from the Kimmswick ("Trenton") in the vicinity of Waterloo, Monroe County, Illinois, and to the east some oil is obtained from the top of the Mississippian rocks near Jackson- ville, and from Pennsylvanian rocks near Carlinville and Staun- ton, Macoupin County, Illinois. The adjoining area in Mis- souri has not produced oil. Previous Exploration Most of the deep wells in the Missouri portion of the area, of which there is any record, have been drilled for water, and are, therefore, not oil tests. It is improbable, however, that any good show of oil would be overlooked even in wells drilled for water, and they may, in a measure, be considered oil tests. Jt should be remembered, however, that water wells are located without regard to structure, so that absence of oil in no way condemns any of the surrounding territory which is struc- turally more favorably located. A detailed discussion of the relations of wells drilled to future prospecting is out of place in a general discussion such as this, and should be considered in more detailed work. In Illinois, the discovery of oil in the Colmar field just east of Hancock County, and the presence of gas in the Pittsfield- Hadley dome have stimulated the search for oil in areas within this State, and a correspondingly greater number of oil tests have been drilled. The approximate location of these wells is shown on the accompanying map (PL I), and the available logs are given in the succeeding pages. All areas, within which detailed structural work has been done, are indicated on Plate I. (54) OIL POSSIBILITIES 55 Review of the Principles of Oil Accumulation In considering the oil possibilities of any area, many factors must be taken into account besides the structure, and it is only after all known factors have been considered that intelligent prospecting can be done. Therefore, before continuing a de- tailed discussion of the oil possibilities and the factors operating to bring them about, a brief review of generally accepted princi- ples is presented. In order that commercial deposits of oil may be formed the source must be adequate and in the productive regions of this continent there are usually heavy beds of carbonaceous shale or thick horizons of limestone that are highly fossiliferous. The matter of adequate source is the prime factor as without it accumulation cannot take place even though structural condi- tions may be perfect. ORIGIN OF OIL Oil and gas are apparently derived from vegetable and ani- mal matter which is buried with the lime, mud, or sands that comprise the rocks. After the carbonaceous matter is once entombed in the rocks and oil is formed, various forces tend to move it about, and under certain conditions concentrate it in local areas, thus giving rise to so-called oil pools. MIGRATION OF OIL The forces or factors most active in the migration of oil are: (1) gravity; (2) gas pressure; (3) capillarity; (4) difference in specific gravity of oil and water; (5) flow of underground waters, and (6) pressure from sedimentation and deformation. (1) Gravity is effective only in dry rocks, in which the pore space is large enough to be overcome by the influence of capillarity. (2) Pressure developed in gas by any means such as heat, chemical action, etc., would tend to cause the gas to expand, and if the pressure became great enough, would force any oil in the surrounding pores to move out ahead of it. (3) Capillary attraction in dry rocks would tend to draw the oil into the finer pores, but if water is present, the greater attraction of the water would cause the water to be drawn into the finer pores, and tend to concentrate the oil in the larger pores. (4) The difference in specific gravity of oil and water in rocks which are 56 MISSISSIPPI VALLEY AREA saturated, or partly saturated, with a mixture of both, causes a separation of the two and a movement of the oil to the top of the water. In tilted rocks, the amount of movement due to this cause may be considerable. (5) In water-bearing rocks, the water does not commonly remain stationary, and under favorable circumstances as when rocks are tilted or folded and exposed at two different levels, there may be a definite artesian circulation, causing the oil to be carried along on top of the water considerable distances to be trapped by higher folds, or flushed out of the rocks entirely. (6) Probably the greatest force in concen- trating the oil eventually in the more porous layers of rock is the increase in pressure on the original oil-bearing strata by deposi- tion of overlying layers of rock or the- diastrophic force which induces folding. The weight of the superincumbent layers, or the pressure causing folding compacts the lower layers, and the oil originally present in the more shaly beds is forced out into the porous sand layers in which the individual grains do not com- pact so readily. ACCUMULATION OF OIL Conditions essential to the accumulation of oil into pools are: (1), a porous stratum which can be made to serve as a reservoir; (2), an impervious covering of rock to retain the oil in the reservoir, and (3), tilting, folding, terracing or other structural modification that will cause large quantities of oil to collect and be retained within a comparatively small area. The reservoir is commonly supplied by sandstone, but any rock which offers sufficient voids is a prospective reservoir. Thus limestones, which have become dolomitized, or fractured, or have been exposed to weathering, or contain porous, granular and oolitic layers have all been known to act as reservoirs. Even shales which are usually too compact to act as reservoirs, may provide a suitable reservoir in exceptional cases, as when fractured along a fault. The cap rock or impervious cover of the reservoirs is generally a shale, but a dense limestone or ce- mented sandstone may serve equally as well. The outlines of the reservoirs are in most cases the result of folding of the rocks. The "lie" of the rocks is known as the structure, the determination of which is exceedingly important in the discovery and development of an oil field. The most favored location for a reservoir depends upon the amount of water contained in oil-bearing rocks. Illinois State Geological Survey. Bulletin No. 45, Plate XVIII. Ist.drill hole 3rd. drill hole >^^. ^€^•0- «=>. •_!_£> .^^X jf • o • o • • o ' * • . .o i^ll&=r^^^ gS^^^^^ Til Drift ;•;•; Sand ^^-^uL^T^" 7 "^^ — '"-r^S^ c 9 1 Miles 2 3 — i Diagram showing conditions governing oil accumulation A. In oil sands saturated with water. B. In oil sands partly saturated. C. In sands containing no water and only partly Idled with oil. OIL POSSIBILITIES 0? In water-bearing rocks, structures of the dome type, long arches designated as anticlines, terraces made by flattening of the dip, or monoclines are all known to be sites of possible reservoirs (PL XVIII). The reason for this is, of course, that after folding, the oil and gas which was once spread out thinly over a wide area, in rising to the top of the water, becomes trapped in these structures and therefore concentrated within a small area. Other factors beside folding, however, may bring about similar conditions. Thus, sand lenses completely surrounded by shale may, even where the strata are flat lying, have enough slope to the upper surface to permit the oil to gather at one end. In tilted rocks where oil-bearing strata are exposed at the surface, the escaping oil may leave deposits of asphalt which effectively seal the outcrop and permit the accumulation of oil immediately behind the outcrop. Rocks once exposed to surface weathering and erosion, become iruore porous and later when buried, may become reservoirs. In faulted regions, the formation of gouge may seal the fault and permit accumulation of oil along the fault zone. In short, any set of circumstances which will cause a concentration of oil or gas from a larger area to a smaller one may produce oil or gas pools. As gravity is the effective migratory force in rocks barren of water, oil will work down the dip of the rocks and collect at the lowest possible place, such as bottom of synclines or sags on the slopes, in positions the reverse of those when the sands are filled with water (PI. XVIII, C). Dry sands, however, are not common in the area here considered. COMBINED EFFECT OF FOLDING AND EROSION After oil has become concentrated in folds there is the possi- bility that subsequent erosion will expose the oil-bearing strata at the surface and incoming fresh waters may flush out the oil from reservoirs near the outcrop. Evidences of Oil and Gas Within the Region Aside from the fact that oil is produced in adjoining regions, there is direct evidence that oil has been, and may be, present within this region. The best evidence of this is, of course, the actual production of gas from the Pittsfield-Hadley dome. Other evidence, however, is furnished by the presence of the oil-bearing shales of the Sweetland Crepk formation; by the thin 58 MISSISSIPPI VALLEY AREA shaly partings at the top of the Plattin limestone, which burn readily when ignited; and by the presence, locally in both the Kimmswick limestone and Edgewood dolomite of small pockets containing black asphaltic residuum. Near Niota, Hancock County, Illinois, a thin, geodiferous layer near the top of the Keokuk limestone contains numerous geodes filled with heavy, black oil, but the surrounding rock is not bituminous. At several localities within the area, drillers of deep wells have' reported shows of oil and gas in the Kimmswick ("Trenton") limestone, in the "Niagaran dolomite," from sandy phases of the Kinderhook and Sweetland Creek shales, and also from the Burlington lime- stone. Probable Oil Horizons The greatest production of oil in Illinois comes from the Pennsylvanian and upper Mississippian formations, but some oil has also been produced from the formations of the lower Mississippian system, the Devonian, the Silurian, and the upper formations of the Ordovician system. In fact, the producing horizons of oil are so widely distributed that no test can be con- sidered complete unless it penetrates the Kimmswick ("Tren- ton"). Nowhere, however, within the State has oil been found below the Kimmswick. Within the area considered, the number of probable oil horizons is less than in the interior of the State, for no upper Mississippian rocks are present; the Pennsylvanian rocks are thin or lacking, and where present they represent the surface rock so that any oil they may have contained once has long since escaped. The Osage and Meramec rocks also outcrop at the surface over most of the area, but these horizons are negative so far as oil production is concerned. Therefore, of the oil producing horizons, only the Kinderhook, the Devonian, Silurian, and upper Ordovician offer possibilities. Factors Affecting Oil Accumulation Within the Area structure As shown in the chapter describing the structure, there are a number of distinct folds which might have caused a gathering and localization of any oil present in the rocks. These, in the order of their size, are the Lincoln fold, the Pittsfield-Hadley OIL POSSIBILITIES 59 anticline, the Adams County terrace, and the minor structurally high areas in Hancock County, Illinois, and Clark County, Missouri. THE LINCOLN FOLD Though possessing many excellent minor structural irregu- larities which might have caused localization of oil, the Lincoln fold can not be considered as a possible oil structure because its crest and slopes expose rocks lower than the Kimmswick. Any oil that may have been present in this structure has long since escaped. For this reason, northeastern Lincoln County, central and eastern Pike County, and all except the extreme western part of Ralls County do not warrant prospecting for oil. In Marion County, where the crest of the anticline plunges to the northwest, and possible oil-bearing strata have an impervious cover, the discovery of doming anywhere along the crest of the axis might be considered favorably. Similarly, any minor folding in western Ralls and Pike counties which interrupt the regional southwest dip might also bear investigation. These possibilities are the only favorable structural features associated with the Lincoln fold, and although reconnaissance work did not offer much promise, a suggestion of a flattening and minor folding was observed in the vicinity of Center, in western Ralls County. PITTSFIELD-HADLEY ANTICLINE The Pittsfield-Hadley anticline shows a distinct doming in Pike County, Illinois, and since some of the probable oil- bearing horizons are present here, under sufficient cover this dome might be considered favorable. Southeast and northwest of Pike County, the axis of the fold plunges gently away from the dome, and other localities which might be considered structurally favorable can be proved only by the discovery of other doming along the crest. No evidence pointing to such doming was observed in this reconnaissance, and can be determined only by detailed work. ADAMS COUNTY TERRACE OR MONOCLINE The broad northward dipping monocline that underlies western Adams County can be considered favorable structure only if detailed work shows it to possess minor folding which might serve to trap any oil migrating up the slope. However, ho prominent folding of this kind was observed. 60 MISSISSIPPI VALLEY AREA MINOR STRUCTURES The higher portions of the minor structures of Hancock County, Illinois, and Clark County, Missouri, should be con- sidered possible oil structures only after drilling has shown production on the more favorable ones farther south. EFFECT OF EARLIER PERIODS OF FOLDING In discussing periods of earlier folding, it was shown that throughout this area there has been continuous tilting to the east, and much to the north. The effect of such tilting, of course, would be to permit the oil to migrate up the dip to the west and south. If then these earlier formations were exposed at the surface after being tilted, any oil they may have contained, except for small quantities as were caught within minor irregular warps and' folds, would have escaped. That the lower rocks, especially the Kimmswick ("Trenton") limestone were exposed at the surface as late as Devonian time is shown in Ralls County, where the Devonian rests on Kimmswick, and in St. Charles County, where the Kimmswick limestone was the surface rock as late as Kinderhook time. These facts are unfavorable to the occurrence of oil in the Kimmswick in this region except in places where the oil might have been retained due to local fold- ing, which trapped the oil and retained it during future folding. CONCLUSION CONCERNING STRUCTURAL FACTORS That the predominating anticlinal fold of the region should expose all the known oil-bearing rocks at the surface is considered unfavorable to large accumulations of oil within the region. The oil-bearing horizons are of necessity barren in the vicinity of their outcrop, but may contain oil in some of the minor folds where they are under sufficient cover to prevent the escape of the oil. Structures most favorable to the retention of oil are, there- fore, minor folds on the slopes of the Lincoln fold, and any doming along the crest of the fold where it plunges in Marion County and farther northwest. The order of importance of these minor structures is: (1) small domes or buckling of the crest of the Lincoln fold from Marion County, Missouri, north- westward; (2) minor anticlines or closures on the slope of the fold in western Ralls and Pike counties, Missouri; (3) Pittsfield- Hadley dome and other closures found along the crest; (4) OIL POSSIBILITIES 61 closures on the Adams County monocline; and (5) closures in the gently folded areas in Hancock County, Illinois, and Clark and Lewis counties, Missouri. The earlier folding in the area, accompanied by exposure of the rocks, is considered unfavorable to the retention of oil except locally, in rocks below the Devonian in the western part of the area, but it is not so important in the eastern portion, which is nearer to the center of the Illinois basin, because folding here was not always accompanied by exposure of the strata. STRATIGRAPHY The presence of bituminous material in all the shale forma- tions and the fact that some of the shales as the Sweetland Creek, will give off oil on distillation, suggest that the shales are probably the original source for most of the oil present within the area. Accumulations of oil should therefore occur in the associated porous rocks. Rocks that might act as reservoirs which are associated with shale formations are: (1) Kimmswick ("Trenton") limestone; (2) local sand lenses at the base of the Silurian (Hoing sand); (3) Silurian limestone and dolomite; (4) Devonian limestones; (5) Louisiana limestone; (6) local sand layers within the Sweet- land Creek shale; and (7) dolomitic layers of the Chouteau and Burlington formations. KIMMSWICK ("TRENTON") LIMESTONE Although the name "Trenton" is in common usage in the oil industry for formations of this horizon, the proper name of this formation in this region is Kimmswick. The limestone is directly below the locally bituminous Maquoketa shale, and the "Trenton" itself shows oil shale partings at the top of the Plattin. Another factor favoring accumulation of oil in the Kimmswick is its porosity, though it diminishes to the north and east where the granular layers become subordinate and are interbedded with dense fine grained layers. Several other unfavorable circumstances beside those due to structure and distribution already mentioned may be noted. Locally, as in northern Ralls County, Missouri, the Maquoketa shale is absent above the Kimmswick. It outcrops at higher levels both to the north and south of the area under discussion, so that there may exist an artesian circulation which would Lend 62 MISSISSIPPI VALLEY AREA to flush out any oil from its path. A suggestion of such circula- tion is found in the apparent decrease in the salinity of water in this horizon from its outcrop northward. Fresh water was found at a depth of 500 feet below the valley flat in the Kimmswick in a well drilled at Warsaw, Hancock County, Illinois, and farther north near Stronghurst, in Henderson County, Illinois, both fresh and salt water are reported from the Kimmswick. Also, where tested under the most favorable structural conditions on the Pittsfield-Hadley anticline the Kimmswick did not yield oil. HOING SAND The Hoing sand is not known from outcrop, and is appa- rently limited in its distribution within this area to the eastern portion, in Hancock and Adams counties, Illinois. So far as known, the sand occurs as discontinuous lenses, and though ideally situated as regards its relations to a shale body, it is an important probable oil horizon over only a small area. SILURIAN LIMESTONE AND DOLOMITE Where the Hoing sand is absent, the porous Silurian dolo- mite of the Alexandrian series is the rock immediately above the Maquoketa, and might serve as an oil reservoir. The unfavorable feature of the Silurian is its limited distribution, for it is present under sufficient cover only in the eastern portion of the area, in Hancock, Adams, and Pike counties, Illinois. DEVONIAN LIMESTONE The Devonian limestone is thin and has about the same dis- tribution as the Niagaran. In the southern portion of the area, it contains sandy beds, both near the top and at the base, but these beds also are under sufficient cover only in the eastern portion of the region here considered. SWEETLAND CREEK SHALE The Sweetland Creek shale is locally sandy near its base, and such sandy phases are excellent prospective oil reservoirs. As much as 8 feet of sandstone have been observed in the Sweet- land Creek shale along Brush Creek in the region where it joins Spencer Creek in southern Ralls County, and the basal portion of shale is also sandy in Pike County, Illinois, where it is exposed in the bluff north of Pleasant Hill. These sandy phases, however, appear to be only local developments. OIL POSSIBILITIES 63 LOUISIANA LIMESTONE The Louisiana limestone is typically a dense, almost litho- graphic rock, entirely unsuitable as a retainer of oil, and although it is possible that it may be locally fractured or contain porous dolomitic beds, it is probably not important as a possible oil- producing horizon. KINDERHOOK SHALE The Kinderhook shale is locally sandy with medium-sized grains and might, under proper conditions, become a reservoir for oil. It is exposed at the surface over most of the southern portion of the area, and exists under cover only in the northern part. HIGHER FORMATIONS None of the higher formations is present here under suffi- cient cover to warrant considering their oil possibilities. Summary of Conclusions The conclusions drawn from a study of the data afforded by this reconnaissance are: (1) That the region does not offer much promise of more than small local production. (2) That the Kimmswick ("Trenton") limestone, which is in general the most promising oil horizon in western and south- western Illinois, is distinctly less favorable to possible production in this region than it is farther south and east. (3) That the most likely oil horizons, aside from the Kimms- wick lenses where they are affected by pre-Mississippian folds, are local sands or sandy phases associated with the Maquoketa, Sweetland Creek, or bituminous phases of Kinderhook shales. (4) That the portion of the region including southwestern Jersey County and southern Calhoun County, Illinois, north- eastern Lincoln County, eastern and central Pike County, and eastern Ralls County, Missouri, is barren territory. (5) That the areas most favorable structurally are: (a) closures on the Lincoln fold where its axis plunges north in Marion and Knox counties, Missouri; (b) a minor fold on the flanks of the Lincoln Fold in extreme western Pike, Ralls, and adjoining counties in Missouri; (c) the Pittsfield-Hadley dome in 64 MISSISSIPPI VALLEY AREA Pike County, Illinois; (d) closures associated with the crest of the Pittsfield-Hadley anticline or Adams County monocline, or the structurally high areas of the northern portion of the area. (6) That local sand lenses at the top of the Maquoketa are present only in the eastern portions of Pike, Adams and Hancock counties, Illinois, and that the sandy phase of Sweetland Creek shales is best developed in western Ralls and probably adjoining regions. (7) That prospecting should be preceded by detailed field and sub-surface work. CHAPTER V— RECORDS OF WELLS DRILLED IN THE MISSISSIPPI VALLEY AREA The following drill records are considered typical for the counties from which they come and will serve to show the char- acter of the rocks encountered in drilling. Correlations of the strata penetrated are those of the writer unless otherwise stated. Because of the difficulty of distinguishing between the differ- ent Ordovician limestones above the St. Peter sandstone and below the Maquoketa shale in drill records, the term "Trenton" is used to include the several limestones. Records of Wells Located in Missouri clark county Record of Missouri Condensed Milk Factory well at Kahoka 1 Thick- Description of strata ness Depth Feet Feet Pleistocene system Soil and yellow clay 15 15 Clay, yellow, drab, and blue 135 150 Sand and gravel 11 161 Mississippian system St. Louis and Ste. Genevieve limestones Limestone, gray 9 170 Sandstone, soft (water) 9 179 Limestone, very fine, gray 51 230 Warsaw-Spergen formation "Soapstone" 60 290 Burlington- Keokuk formation Limestone 110 400 "Fire clay" 6 406 Limestone with chert , 66 472 Kinderhook series Hannibal and Grassy Creek (Sweetland Creek) shales "Soapstone," blue 30 502 Sandstone, bluish 9 511 Shale, blue gray 126 637 "Soapstone," ash color 20 657 Shale, brown 25 682 »Wilson, M. E., The occurrence of oil and gas in Missouri: Missouri Bur. of Geol. and Mines, Vol. XVI, 2nd ser., p. 97, 1922. 5 (65) 66 MISSISSIPPI VALLEY AREA Record of Missouri Condensed Milk Factory Well at Kahoka — Continued Thick- Description of strata ness Depth Feet Feet Silurian-Devonian systems not present Ordovician system Maquoketa shale Shale 85 767 "Trenton" limestone Limestone 293 1060 St. Peter sandstone Sandstone 131 1191 Although no Louisiana limestone is shown in this log it is probable that this limestone is present, at least in the eastern portion of the county. The Silurian-Devonian rocks are absent over most of the county, but may be encountered in the extreme western part. . LEWIS COUNTY Record of the Canton Oil and Gas Company well No. 2 in the SW. \i NW. % sec. 14, T. 62 N. f R. 6 W* Thick- Description of strata ness Depth Feet Feet Pleistocene system Loess, clay, and shale 40 40 Mississippian system Burlington- Keokuk (includes some Warsaw) formations Limestone, blue to gray, crystalline, white and blue chert 100 140 Limestone, fine grained, gray-blue 80 220 Limestone, medium grained, gray, blue, white chert. 60 280 Kinderhook series Hannibal shale Shale, gray, uniform 50 330 Shale, sand, greenish . 40 370 Louisiana limestone Limestone, gray, brown, fine grained 50 420 Grassy Creek (Sweetland Creek) shale Shale, bluish gray 40 460 Silurian-Devonian systems not present Ordovician system Maquoketa shale Shale, clayey, dark gray 20 480 No record 65 545 •Idem, p. 96. RECORD OF WELLS 67 Record of the Canton Oil and Gas Company well No. 2 in the SW. % NW. \i sec. 14, T. 62 N., R. 6 W— Continued Thick- Description of strata ness Depth 1 Feet Feet Ordovician system — Continued "Trenton" limestone Limestone, light to dark gray, fine grained, more crystalline towards base 175 720 Limestone, light gray, very hard, fine grained 30 750 Limestone, magnesian, fine grained, brown and hard. 60 810 No record 70 880 Limestone, almost non-magnesian : 15 895 St. Peter sandstone Sandstone, white, coarse graiujd 33 928 The above log is typical for most of the county, but to the west and especially the southwest, limestones of Devonian age may be expected between the Maquoketa and Grassy Creek (Sweetland Creek) shales. The limestone at 370 feet is somewhat thicker and lower in the section than would be expected from a study of the outcrops farther south, but this may be due to an error in logging the well. LINCOLN COUNTY Record of Prairie Oil and Gas Company well at Moscow Mills* Thick- Description of strata ness Depth Feet Feet Pleistocene system Soil and clay 8 8 Hardpan, yellow 4 12 Pennsylvanian system (?) Soapstone, blue 40 52 Mixed gravel (water) 3 55 Mississippian (?) system Sandstone, white, hard 25 8Q> Keokuk-Burlington and Chouteau formations Limestone, brown, cherty 260 340 Hannibal and Maquoketa shale with possibly some Devonian Soapstone, blue, soft 10 350 Limestone, brown 72 422 Shale, brown . 3 425 Kimmswick ("Trenton") limestone Limestone, brown and white 95 520 Sandstone, yellow, hard 15 525 Limestone, brown, hard 126 661 St. Peter sandstone Sandstone 79 740 » Idem, p. 100. 68 MISSISSIPPI VALLEY AREA Record of William Overall well in SE. }4, sec. 1, T. 49 N., R. 1 E. Thick- Description of strata ness Depth Feet Feet Pleistocene system Soil, light, ashy 2 2 Hardpan 3 5 Clay, light brown 10 15 Soapstone, gray streaks of sand 27 42 Pennsylvanian system Soapstone, dark blue 94 136 Mississippian system Burlington-Chouteau formation Limestone, brown ' 54 190 Limestone, blue. 30 220 Hannibal shale Shale, dark 35 255 Ordovician system Maquoketa shale Shale, dark blue 40 295 "Trenton" formation Limestone, gray 155 450 Limestone with shale '. . . . 115 565 Sandstone, hard 12 577 Limestone, gray 18 595 St. Peter sandstone Sandstone 61 656 In correlating the above log the writer took the liberty of separating the 75-foot dark shale formation into two portions, the upper 35 feet of which is referred to the Hannibal, while the lower portion is referred to the Maquoketa. The separation is based on observations of outcrops about a mile northwest of the well which show Hannibal shale resting on Maquoketa. Locally in this same vicinity Devonian limestone as much as 12 feet thick comes in between the Hannibal and Maquoketa shales. MARION COUNTY Record of well at Palmyra Thick- Description of strata ness Depth Feet Feet Mississippian system Burlington limestone Limestone, brownish 20 20 Limestone, finer 11 31 Kinderhook series Hannibal (?) formation Sand, gray 34 65 RECORD OF WELLS 69 Record of well at Palmyra — Continued Thick- Description of strata ness Depth Feet Feet Mississippian system — Continued Louisiana limestone Limestone 25 90 Grassy Creek (Sweetland Creek) shale Clay, light blue 70 160 Silurian-Devonian systems missing Ordovician system Maquoketa shale Clay, dark olive, little limestone 125 285 ("Trenton") limestone Limestone, dove color 15 300 Limestone, light gray, compact 55 355 Limestone, compact, dove color. 15 370 Limestone and quartz (?) crystals 190 560 Limestone, impure light and dark gray 40 600 St. Peter sandstone Sand, fine 100 700 It is probable that some of the shale included in the Ma- quoketa belongs with the Kinderhook. While the above log will serve to give an idea of the character and thickness of the forma- tions in the eastern portion of the county, it is known from out- crops and well records that in the western portion of the county the Devonian system is present and is represented by limestone which may reach a thickness of 80 feet or possibly a little more. The following logs from the vicinity of Nelsonville in north- western Marion County and from the Jacksonville well at Monroe City in eastern Monroe County afford a general ide'a of the strata penetrated in drilling to the St. Peter sandstone in western Marion County. Record of C. H. Mohr well near Nelsonville in sec. 21, T. 59 N., R. 8 W* Thick- Description of strata ness Depth Feet Feet Pleistocene system Clay 45 45 Mississippian system Kinderhook series Hannibal shale Shale, blue 150 195 Louisiana limestone Limestone 60 255 Grassy Creek (Sweetland Creek) shale Shale, gray 35 290