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 State of Illinois 
 Department o.: Registration and Education 
 STATE GEOLOGICAL SURVEY DIVISION 
 John C. Frye, Chief 
 
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 GEOLOGICAL SCIENCE FIELD TRIP 
 
 Sponsored by 
 
 ILLINOIS STATE GEOLOGICAL SURVEY, UR3ANA 
 
 <33DUM¥<DW AVERE& 
 
 Jersey County 
 
 Jerseyville, Hardin, St. Charles, and Brussels Quadrangles 
 
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 Leaders 
 George M. Wilson and I. Edgar Odom 
 Urbana, Illinois 
 May 7, 1960 
 
 GUIDE LEAFLET 1960B 
 
 HOST: Grafton School 
 
GRAFTON GEOLOGICAL SCIENCE FIELD TRIP 
 
 Itinerary 
 
 0.0 0.0 Assemble at southeast come, of Grafton School. Enter Rt. 100. Continue 
 
 east to stop sign. 
 
 i **■ «„ Pt- inn At Grafton numerous specimens of triiobites 
 °' 1 ° A ^\ e rfon irroc^Tf'sitrLage. At present however, they are 
 
 hard to find. Continue north on Rt . 100 up Jersey Hollow. 
 
 0.2 0.3 Note outcrop of loess on the left. 
 
 *-u^ laff TVif Silurian System at Grafton 
 
 - °- 5 s con £ts of sia^ssra^r^i^^"-- -* * «— 
 
 thickness of 105 feet. 
 
 , , ,-v,^ y-ccrhf Specimens of cystoids have been found 
 1 0.6 Silurian dolomite on the right, specimens uj. y 
 
 here. 
 
 0.2 0.8 Note that a landslide has occurred on the left. 
 
 « «. * , hp q-iiurian Svstem The Silurian is overlain by the Devonian 
 0.4 1.2 The top of the Silurian System over lain by the Mississippi™ 
 
 Cedar Val ey Limest on.. Thl i rn i Hannibal 
 
 Sylamore Sandstone (4 inches;, oien "*« c P( ioHii Limestone (7 feet); 
 Shale (25 feet); Chouteau Limestone (55 feet); Sedalia Limestone y i 
 lern Glen Limestone (20 feet); and the Burlington Limestone (45 feet). 
 
 0.1 1.3 Hannibal Shale on right. 
 
 0.1 1.4 Chouteau Limestone on right. 
 
 0.1 1.5 Sedalia Limestone on right. 
 
 0.1 1.6 Fern Glen Limestone on right. 
 
 0.1 1.7 Burlington Limestone on left. 
 
 0.1 1.6 The last of the Mississippian outcrops. Loess mantles the remainder of 
 
 the upland. 
 0.5 2.3 Crest of the hill. Note the rounded character of the upland which is 
 
 mantled with loess. 
 
 In the Pleistocene Period (or "Great Ice Age") North *«ica 
 experienced four successive glacial invasions, each separated by long 
 intervals of mild climate. Of these four invasions tne earliest the 
 Nebraska*, may have extended southward to the vicinity of «»-*£ 1 ^ 
 Pike County. The second, or Kansan invasion, moving down from the re io 
 east of Hudson Bay, extended over the area east of Grafton. 
 
 When the Kansan ice sheet melted away it l e « p ^ d b ^5or" 8 itre 
 glacial drift which mantled the surface and concealed the bedrock There 
 followed a long interglacial interval (the Yarmouthian Age) which v ^ 
 °t record In the form of old soils and weathered zones in ^ Kans« *# 
 elacial drift From the amount of weathering and leaching that attecteo^ ^ ^ 
 8 tne Kansan drift, the length of the Yarmouthian Age is estimated from ^/^v 
 200,000 to 300,000 years. ^ cu 
 
 v" 
 
Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 University of Illinois Urbana-Champaign 
 
 http://archive.org/details/guideleafletgraf1960illi 
 
- 2 - 
 
 The Yarmouthian Age ended with the advance of a new glacier from a 
 center east of Hudson Bay. This glacier, called the Illinoian, covered 
 nearly all of Illinois. Its western edge coincided closely with the 
 western boundary of the state. Grafton is within two or three miles of 
 the western limit of Illinoian glaciation, which here extended a few miles 
 into Missouri. 
 
 After several thousand years, the climate warmed causing the 
 Illinoian Glacier to melt away. During this warm age, the Sangamonian, 
 the upper part of the Illinoian till was weathered and soils developed, 
 as in the preceding Yarmouthian interval. However, the Sangamon Soils are 
 less intensely weathered than the Yarmouthian Soils, so the Sangamonian 
 weathering interval is estimated to have lasted only about 150,000 years. 
 
 The Sangamonian Age ended when the fourth and final readvance of the 
 glaciers occurred. This glacier, called the Wisconsinan, never reached 
 the Grafton area. However, the Mississippi and other streams were choked 
 with sediment washed out from the ice that stood to the north and east. 
 The frigid blasts that whipped across these broad sand and mud flats blew 
 dust over the uplands, covering the Illinoian drift and the Sangamon Soils 
 with a thick layer of loess. The loess is an important component of 
 present-day soils in the Grafton area. 
 
 2.0 4.3 Note the high ridge to the left, at a distance of about three quarters of 
 a mile. This is an Illinoian morainal ridge. 
 
 0.9 5.2 SLOW. Turn right (south). Entering the Elsah blacktop road. 
 
 0.3 5.5 Note the good conservation practice on the hill on the far right, where 
 there are grassed waterways on the steeper portions of the hill. 
 
 0.4 5.9 Note the grassed waterways. 
 
 0.5 6.4 Note the sinkholes on the right. Sinkholes are common features of regions 
 underlain by limestone bedrock. 
 
 0.8 7.2 SLOW. Turn right on road to Chautauqua. 
 
 0.1 7.3 Sinkholes on right and left. 
 
 0.1 7.4 Note the loess on the upper portion of the hill with the soil profile 
 
 developed in the upper five or six feet of loess. Note the chert pebble 
 band immediately beneath it and overlying some 15 to 18 feet of deeply 
 weathered Illinoian till. At the base of this cut is an outcrop of 
 Mississippian limestone of Burlington age. West of this exposure note the 
 great accumulation of cherty residuum on the north side of the road. The 
 Burlington in this section of the country is quite cherty. 
 
 0.8 8.2 SLOW. Enter the New Piasa Chautauqua Grounds. Follow the main road into 
 the Chautauqua Grounds area. 
 
 0.3 8.5 Stop 1A. Chautauqua Spring. Unconformity between the Chouteau and 
 Sedalia Limestones. 
 
 Lower Mississippian strata of Valmeyer and Kinderhook age are well 
 exposed in the cliffs that border the Mississippi River in the vincinity 
 of Chautauqua. The section exposed above the spring at Chautauqua is of 
 special interest because it reveals an unconformable surface between the 
 Chouteau Limestone of Kinderhook age and the Sedalia Limestone of 
 Valmeyer age. 
 
- 3 - 
 
 The tilted Chouteau Limestone was originally deposited in a horizon- 
 tal position. Follov7ing its deposition this region was disturbed by a 
 mild deformation which tilted the Chouteau beds toward the north. Erosion 
 planed off the tops of the tilted beds, and later the Sedalia Limestone 
 was laid down horizontally upon these tilted beds. 
 
 An unconformity is an important criterion used to divide the rock 
 column into units of different ages. Usually unconformities indicate 
 that a region was raised above sea level and subjected to weathering and 
 erosion. The unconformity exposed here between the Choteau and Sedalia 
 Limestones marks the boundary between the Kinderhook and Valmeyer Series 
 of the Mississippian System, and indicates that at least in this local 
 area there was a period of erosion between the deposition of the Chouteau 
 and Sedalia Limestones. The unconformity is very local, for only a few 
 miles to the north no unconformity can be recognized. 
 
 Chautauqua lies near the margin of the Illinois Basin. Unconformi- 
 ties usually are abundant near the margins of sedimentary basins because 
 the seas were often shallow or not present at all, while in the deep 
 portion of the basin seas were present almost continuously. When 
 geologists attempt to trace unconformities into the Illinois Basin, they 
 find that most of them disappear. 
 
 Springs are often seen in areas underlain by limestone bedrock. 
 Springs are fed by rain water that goes underground through joints and 
 crevices in the limestone. This water cannot penetrate lower than the 
 water table, which usually is determined by the major streams in the area. 
 This spring emerges at about the level of the Mississippi River along a 
 well-developed joint plane. 
 
 0.0 8.5 Turn around. Retracing route to Rt. 100. 
 
 0.3 8.8 STOP. Turn left (north). 
 
 1.9 10.7 Stop for Rt. 100. Turn right (east). Continue across the Jersey County 
 upland. 
 
 1.5 12.2 Note the grassed waterways on the left. 
 
 0.2 12.4 Note the outcrop of the Salem Limestone on right and left. 
 
 1.1 13.5 Note the outcrop of the Salem Limestone in the stream on the right. 
 
 0.1 13.6 Note the Salem Limestone en the left. 
 
 0.3 13.9 STOP. Turn left. Enter Rt . 109. CAUTION. 
 
 0.9 14.8 SLOW . 
 
 0.1 14.9 Turn left to Dow (west). We are approaching a morainic remnant of 
 
 Illinoian age some 70 feet high. This particular spot allows an excellent 
 view of the Jersey County countryside, especially of the moraines that are 
 here. The surface is loess covered and the soil developed in the loess. 
 
 0.9 15.8 Stop IB. Discussion of Illinoian Glaciation. 
 
 On this hill the loess and till have a combined thickness of more 
 than 100 feet while on the general upland surface they have a thickness of 
 less than 60 feet. This knoll may be identified as a morainal feature 
 
- 4 ■> 
 belonging to a series of similar knolls in this section oi the country 
 with a northwest-southeast trend. The margin of the Illinoian was not 
 far west of this spot--possibly only three or four miles. 
 
 ).3 lo.l SLOW. Crossroads. Turn left (south). 
 
 3.6 16.7 SLOW. Turn right (west). 
 
 0.1 16.8 SLOW. Turn left (south). 
 
 0.3 17.1 Note the outcrop of the Warsaw Shale on the right and left. 
 
 0.2 17.1 Stop 2. Walk to Rt. 100. Go to the right, descending toward the stream. 
 The limestone along the roadcut is the Salem Limestone, the same lime- 
 stone that is extensively quarried in southern Indiana for use in the 
 building of houses in the Middle West. This is the best outcrop of the 
 Salem in the Grafton area. Here it is 15 to 18 feet thick and very pure. 
 However, cavities filled with calcite are found in this section of the 
 country. In the stream bed is the Warsaw Shale, which in western Illinois 
 contains many geodes . The Warsaw here contains geodes filled with min- 
 erals, such as quartz, chalcedony, calcite, chalcopyrite, malachite, 
 kaolinite, dolomite, and ankerite. The origin of these geodes is un- 
 certain. 
 
 5.1 22.2 Start descent of Jersey Hollow, traversing the geological column beginning 
 
 with loess at the top, accumulated cherty residuum on top of bedrock, and 
 the Mississippian, Devonian, and Silurian Systems. 
 
 0.8 23.0 Note the cavern in the Hannibal Shale. 
 
 1.2 24.2 STOP. Turn right on Rt. 100. 
 
 0.2 24.4 Silurian dolomite on the right. Note the massive characteristics of this 
 dolomite. 
 
 0.7 25.1 Note the combined thickness of the Silurian dolomite and the overlying 
 
 Mississippian rocks. The first big ledge, about 80 to 90 feet above the 
 level of the road, is the top of the Silurian System. 
 
 0.6 25.7 Note the buildings on the ri ht built with Silurian dolomite. 
 
 0.2 25.9 The Father Marquette Memorial commemorates the first recorded entrance in 
 1673 of white men into the Illinois country. In the spring of 1673, 
 Louis Joliet and the Jesuit priest, Father Jacques Marquette, were sent 
 by che French Government over the Wisconsin portage to explore the 
 Mississippi River for a passage to the Pacific Ocean. They travelled as 
 far as the Arkansas River, where they turned back. In September they 
 entered the Illinois River, making camp at this spot. Father Marquette 
 noted the event in his journal on the trip, thus making it the first 
 recorded entrance of white men into the Illinois country. 
 
 0.6 26.5 Note the Silurian dolomite, dipping to the north. Geologists believe the 
 rocks here are inclined in this direction because of slumping. 
 
 0.9 27.4 Note the very steep (about 75°) south dip of the rocks here. 
 
 0.2 27.6 The rocks here dip at an angle of more than 65 degrees south. 
 
 0.1 27.7 Here the rocks dip about 45 degrees south. 
 

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 .2 27.9 Note the well-developed joints and the slickensides developed on the 
 bedding planes. 
 
 ,.1 2G.0 Stop 3. Discussion of the intense folding of the rocks and structures on 
 the Cap au Gres Structure. 
 
 After considerable discussion, geologists have decided that the rocks 
 here shall be tentatively identified as Ste. Genevieve. According to the 
 United States Geological Survey Professional Paper 218, William W. Rubey, 
 1952 they are Keokuk, while others have lumped them into the Valmeyer 
 Series of Mississippian age. As early as 1947, Dr. Raasch identified 
 these rocks as Ste. Genevieve. The reason for this uncertainty of cor- 
 relation is that this is an isolated outcrop in a faulted and folded 
 structure, and no continuity can be assured. 
 
 A few hundred feet west the rocks in Deer Creek Hollow are of 
 Ordovician age of the Kimmswick Formation. 
 
 Note the slickensided surfaces on bedding planes, crumpling of 
 incompetent beds, faulting, and mineralisation. The structure of the 
 Cap au Gres Fold is most striking. 
 
 1.1 29.1 Note the upper terrace surface in the pasture on the right, some 40 feet 
 higher than the road level. 
 
 0.8 29.9 SLOW. Enter the Pere Marquette State Park picnic area No. 1 for lunch. 
 
 Stop 4. Lunch. We will not go into the park, because time will not 
 permit us to make the long trip, or series of trips, that would be 
 necessary to learn of all of the geology in this park. We suggest, 
 however, that you might make trips on foot some other time. The lunch 
 area, as well as the Lodge, are on the Deer Plain terrace of Wisconsman 
 age. You may follow the trails according to the plan shown on the pre- 
 ceding page. 
 
 Suggested Stops in the Park 
 
 Stop 4A. Kimmswick and Maquoketa Formations (Ordovician). 
 
 The oldest rocks exposed in the Pere Marquette Park are of Middle 
 Ordovician age. The Kimmswick Formation outcrops in small exposures 
 along Rt. 100 north of the park entrance. The formation is approximately 
 70 feet thick in the vicinity of the park, but only a few feet are easily 
 visible. The limestone is exceptionally pure and is gray-white in color. 
 Upon weathering, the rock becomes quite rough on outcrop surfaces allow- 
 ing lichen to gain an easy foothold. The Kimmswick on fresh fractures 
 has a highly petroliferous odor, and only a few miles away (at Dupo and 
 Waterloo) it produces oil. 
 
 Lying above the Kimmswick is the gray-green, weak, dolomitic, platy 
 Maquoketa Shale. This shale weathers readily and gives rise to rather 
 gentle slopes which are often tree covered. In some places dolomite beds 
 are found in this shale. 
 
 The Maquoketa is unconformably overlain by an 80-foot section of 
 Silurian dolomite exposed at a place called Goat Cliff. The Silurian is 
 in turn unconformably overlain by the gray, silty Hannibal Shale. At 
 
7 - 
 
 u a „* rnat Cliff 600-800 feet from Twin Springs, the Silurian 
 f;j::t dip southward'^ the Gap au Gres Monocline. H» outcrops are 
 marked, however, by slump, talus and loess. 
 Stop U. twin Springs (Silurian, Devonian, and Mississippian Systems). 
 
 Th e Silurian dolomites are ^-/-^Af d^grees'so^: 
 , t riain S approx^ately east T st an^drpp n^out^S^ , The 
 
 s riL:: %L 5 JZ "- bU t ^-pp-xi^ 8 ^: regies 
 
 STSSS^ulCr^lS ^ - — - strongly faulted 
 with special features to be seen. 
 
 I„ this series of Silurian rocks , '^^^ ^^S^ 
 S 5^^L^ rt ££iSr=. C Sr=^«i-*4 C-saran, is 
 
 represented by the Joliet Dolomite. 
 
 The Middle Devonian Cedar Valley 1 ^ t " i ^J^ 1 S i i!i£ 
 erous limestone and the lower Missi "*»*»<££• ^f^nd in the im- 
 also are found. Rocks occurring in three systems 
 mediate area of Twin Springs. 
 
 c a <n fhiq series of outcrops, geologists con- 
 From the evidence found ^ * *!n " fres structure at more 
 elude that there was movement along ****™^J££™ t -Devonian 
 than one time, but specifically movement occurred during p 
 and pre -Mississippian time. 
 
 Stop 4C. Lookout Point physiographic study. 
 
 *u TiUnrM'^ River toward Calhoun County. The 
 ^^JTSSTS.^ K^s. river whereas they 
 rise nearly 450 feet above the river on the Jersey uou y 
 
 Across the river to the west is the Beer Plain ^H^^ slopes 
 Wlsconsinan Age of glaciation, the Valderan Sub-age **£" ? he 
 
 approximately 15-20 fee, : per mUe away rom he^base £ ^^ o£ 
 next terrace ^J 6 ^^ 6 ^/^ "ily seen from Oreenbay Hollow, which xs 
 8 de a v C ei:pe°d n ;n ST cre^of the Cap au Gres - Lincoln Anticline. 
 
 The upland surface in this section of the country has been identified 
 by Rubey (1952, Geology and Miners «■£•££***? ?j£ e with the 
 Quadrangles) as a .peneplaxn surface. ^ c °f£ rttaeitern niinois, south- 
 Lancaster Peneplaxn of the Driftless Area or sur f a ce area 
 western Wisconsin, and northwestern Iowa. On this upl 
 cherry gravels are widespread and may be of Tertiary age tur 
 
 „, ..» -suss ass ^S^r£S£T 
 
 Cap au Gres Fold, geologists would , deposition of the brown 
 Paper 218), that folding continued after the deposicio 
 
 chert gravels. 
 
 Stop 4D. Mississippian (Warsaw) geodes. 
 
.,..,» i- - ie-o re-entrant in the bluff 
 South of the shelterhouse there is ^ P che Cap au Gr£S 
 
 line which marks the position o. «*»"?" u and because of folding, 
 Structure. Because of the »* '£,*£„ are many geodes (rounded 
 the shale does not show at the ^ c ^> x ized by collectors, because 
 
 . ■ • n m pcf Q ne (Salem and Lower St. Louis). 
 Stop 4E. Mississippian limestone ^aie 
 
 a -,-imoct- entirely of the shell 
 The Salem Limestone here is compose almost »' * ^ ^ ^ ^ 
 remains of minute animals that lived during the P steeply dipptng 
 stone The rock outcrops along a trail in a b, 
 outcrop Just south of the Warsaw re-entrant. 
 
 South of this ridge the St. Louis Limestone outcrops. 
 
 , < • ,.„ st Louis Limestone and Upper St. Louis and pos- 
 Stop «. Mississippian St. Louis 
 sibly Ste. Genevieve Limestones. 
 
 At this stop, the trail descends past a nearly complete section^ 
 the St. Louis Limestone. The ™J«^*^S ^lithographic lime- 
 composed of angular fragments of fine "Icar boulders . Th i s breccia 
 
 Sr^rS'tSrS SStS C! northeastern Missouri, and 
 western Illinois. 
 
 . .. • c™* 70 feet of limestone can be seen along 
 Overlying the breccia > some 70 feet o ^.^ ciosely r£ _ 
 
 the trail to the museum. The upper por^u 
 
 sembles the rocks found in Stop 3. 
 
 i-hp st Louis is quite fossiliferous , and some of the 
 Ir some zones, the St. Louis ij> h« 
 fossils include corals and brachiopods. 
 
 Stop 4G. Pleistocene and Physiography. 
 
 , kfl urnRsels Terrace, which is composed of 
 
 The lodge is ^-f/ - t ^ s B ^ S J! ed in a lake when the ice of the 
 interbedded sand and silt that was a p ^ vicinity of 
 
 Illinoian Glacier blocked the Mississippi * 
 St. Louis. 
 
 The Deer Plain Terrace (Rubey, 1952 Prof Paper 218 P. D0-96M. 
 . valley train deposit of lat . « scons nan Val deran) ^ ^^ q£ 
 
 Valley. 
 
 0.2 30.1 T-road east. Turn left (south). 
 
 0.1 30.2 STOP. Enter Rt. 100. Turn right (west). 
 
 0.3 30.5 Note the Pere Marquette Lodge on right. 
 
 0.3 30.3 Note the inclination of the rock f ^J^^^^^^V^^' 
 tenths of a mile. Shear zones and ^»^~^J \ n the formation of the 
 these rocks attest to the ""^ ^^^fold* Occasionally, the 
 Cap au Gres Fold. This structure is a faulted roi 
 
- <■» - 
 
 v, in this section are standing vertically, although the average dip of 
 Z locL in this Portion of the fold ranges fro, 20 to 75 degrees. 
 
 w 31 2 Note the limestone on the right; this is the Kimmswick Ltaestone of 
 '"* ordovician age. This limestone is overlain by Maquoke.a .hale. 
 
 0.« 31.6 Note the talus blocks of Silurian dolomite. 
 
 o'.2 31.8 On the right, note the Maquoketa Shale, a greenish, buff-colored, fine- 
 
 grained shale. 
 0.3 32.1 Stop 5. Deer Plain and Brussels Terraces. 
 
 Terraces formed by deposition of glacial outwash during the retreat 
 of PlS™ cTiers'from Illinois and adjacent areas are very «-..- 
 
 ous alonp the Illinois and Mississippi Valleys m this area, ine low 
 
 This lower terrace here is called the Deer Plain * e " 
 
 of Deer Plain in southern Calhoun County where the terrace is develop 
 
 extensively. 
 
 T he Deer Plain terrace ^^^^J^^ZSL^T " 
 
 The age and origin of the Deer Plain Terrace is still ««*•»*"•?• 
 William W^Rubey wrote in Professional Paper 210 on *J-1«- the 
 Hardin and Brussels quadrangles tb.tJb.De ^/^^ and 
 
 Illinois Valley was formed as a result oi uc P 
 gravel across the mouth of * , lUinoi, ^- n^he Ute^rt of*^ 
 
 sand filled in the entire valley to the upper level of the Deer Plain 
 
 Terrace. 
 
 i.: 
 
 33.6 
 
 0.3 34.5 
 
 A short distance to the east is another prominent terrace which also 
 occurs extensive "along the Illinois and Mississippi Valleys in this area. 
 tITs terrace is older than the lower Deer Plain Terrace and is called the 
 Brussels Terrace for the town of Brussels in southern Calhoun County. It 
 occurs at 480 to 540 feet above sea level and was formed during the 
 lUinoian Ige of S-iat ion when a tongue of the ice extende ^across the^ 
 
 f r ::: s d ip a p iarin ^r^; n r ^^ - rr 
 
 in which silt and sand was deposited to the upper level of this terrace. 
 
 .u- c ar . ripht The limestone quarry 
 
 of silt, sand, and gravel accumulated in the vaiiey omy 
 to more recent erosion. 
 
 *.u~ OQ K-iiir The veeetation is peculiarly 
 rda P tea%o e thiToess g so a ils: n xS^.s^'bl^o^of the Illinois Valley 
 
 during the Pleistocene Epoch. 
 
- 10 
 
 .4 35.9 Road to Rosedale. Continue ahead on Rt. 100. 
 
 ).2 36.1 Outcrop of Silurian dolomite on the right. Northward, because the rocks 
 dip to the north, progressively younger and younger rocks are exposed in 
 the valley wall. 
 
 1.3 37.4 Note the carving in the loess bluff on the right. 
 
 1.1 38.5 Note hill prairies directly ahead. These are typically shown here. 
 
 0.4 33.9 Stop 6. Nutwood. Leave car along Rt. 100. A few yards east of Rt. 100 
 on a limestone roadway, there is an interesting Devonian and Silurian 
 section, which is as follows: 
 
 Pleistocene 
 Loess 
 Devonian 
 
 Cedar Valley Limestone, gray in color and with in- 
 clusions of shale, many fossils, including corals 
 and brachiopods 
 
 "Hoing" Sandstone, medium to coarse grained with 
 evidence of secondary growth of the grains, some 
 doubly terminated quartz grains 
 
 Silurian 
 
 Dolomite, buff to tan, granular, hard 
 
 Feet 
 10 plus 
 
 Ik 
 
 0-2 
 
 8-10 
 
- 11 - 
 
 The Cedar Valley Limestone of Devonian age is quite fossiliferous . Many 
 large corals and brachiopods are found in it. Note the irregular contact 
 of the Devonian on the Silurian here. This is one of the greatest uncon- 
 formities, in terms of length of time represented, present in the geologic 
 column of Illinois. 
 
 1.8 39.7 Note the terrace remnant over which the road passes and the broad expanse 
 of the Illinois River Valley on the left. 
 
 3.4 40.1 Note the relative lack of talus along the east bluff of the Illinois River 
 Valley. As previously noted, this is due to the great amount of erosion 
 that took place in the Illinois Valley during the Pleistocene. 
 
 0.3 40.4 SLOW. Turn right. 
 
 0.1 40.5 STOP. Enter Rt. 16. CAUTION. 
 
 0.1 40.6 SLOW. Turn left. 
 
 0.2 40.8 Ford stream with CAUTION. Rocks on the right and left are of Devonian 
 Cedar Valley Limestone. 
 
 0.1 40.9 Stop 7. Outcrops of Devonian Cedar Valley Limestone, Devonian or 
 
 Mississippian Sylamore Sandstone, Mississippian Louisiana Limestone, 
 Glen Park Siltstone, and Hannibal Shale. 
 
 Miss. Hannibal Sh. 
 
 Miss. Glen Park Ss. 
 Miss. Louisiana Ls. 
 
 "T 
 
 Dev.-Miss. Sylamore S3. 
 
 (fossiliferous) 
 
 Dev. Cedar Valley Ls. 
 
 (fossiliferous) 
 
 This is one of the best exposures of the Devonian Cedar Valley Lime- 
 stone in the field trip area. The upper beds of this formation are a 
 dark gray, fragmental limestone crowded with fossils of many varieties. 
 The thin sandstone overlying the Cedar Valley, which is the resistant bed 
 at the top of the small waterfall, also contains numerous fossils. A 
 short distance upstream, a fine-grained, light yellowish, sublithographic 
 limestone is encountered. This limestone is called Louisiana for Louisi- 
 ana, Mo., where the formation was defined in 1892. Further upstream, 
 Hannibal Shale is exposed in the creek bank. 
 
FORMATIONS AND REMARKS 
 
 ERA 
 
 Cenozoic 
 
 Quaternary 
 
 Pleistocene 
 
 See 
 
 Pleistocene Time Table 
 
 Mesozoic 
 
 Paleozoic 
 
 Jurassic 
 
 Triassxc 
 
 Permian 
 
 Pennsylvanian 
 
 Devonian 
 
 Silurian 
 
 Ordovician 
 
 Cambrian 
 
 Precambrian 
 
 Chesterian 
 
 Mississippian Valmeyeran 
 
 Kinderhookian 
 
 >er 
 
 Lov;er 
 
 Pre-glacial gravels of 
 polished ^^___________— 
 
 Present in extreme southern 
 I llinois only 
 
 Not present in Illinois 
 Not present in Illinois 
 
 Ste. Genevieve Ls. 
 
 St. Louis Is. 
 
 Warsaw Sh. 
 Keokuk-Burlington Ls. 
 
 Spdalia Ls._ 
 
 _b^s^_of_SJjAirian. 
 
 Kitnmswick Lis. Outcrops in 
 pere Marquette area 
 
 No data 
 
 available 
 No data available 
 
 No 
 
 data available 
 
r 
 
 TIME TABLE OF PLEISTOCENE GLACIATION 
 (after J. C. Frye and H. B. Wiltaan, I960) 
 
 STAGE 
 
 SUB STAGE 
 
 RECENT 
 
 Years 
 Before Present 
 
 NATURE OF DEPOSITS 
 
 SPECIAL FEATURES 
 
 5,000 
 Valderan 
 
 11,000 
 
 Twocreekan 
 12,500 
 
 Soil, youthful profile 
 of weathering, lake and 
 river deposits, dunes, 
 ■peat 
 
 Outwash along 
 Miss^sij3pJ L _VaJj£y_ 
 
 Peat and alluvium 
 
 Ice wil 
 
 z co 
 < «h 
 
 z u 
 
 J-4 <0 
 </> .-< 
 Z 00 
 
 8* 
 h <r 
 
 3 N^ 
 
 Woodfordian 
 
 22,000 
 
 Farmdalian 
 
 Drift, loess, dunes, 
 lake deposits 
 
 SANGAM0NIAN 
 
 (3rd interglacial) 
 
 28,000 - 
 Altonian 
 
 50,000 to 
 70,000 
 
 Soil, silt and peat 
 
 Drift, loess 
 
 . thdr awal^_^rosion 
 
 Glaciation, building of 
 many moraines as far 
 south as Shelbyville, 
 extensive valley trains, 
 outwash plains, and 
 
 Ice withdrawal, weather- 
 ing, and erosion 
 
 Glaciation in northern 
 Illinois, valley trains 
 along major rivers, 
 Wijinebjgo_drift _ 
 
 Soil, mature profile 
 of weathering, al- 
 luvium, peat 
 
 ILLINOIAN 
 (3rd glacial) 
 
 Glaciers from northeast 
 at maximum reached 
 Mississippi River and 
 nearly to southern tip 
 of Illinois 
 
 YARM0UTHIAN 
 
 (2nd interglacial) 
 
 Soil, mature profile 
 of weathering, al- 
 luvium, peal 
 
 KANSAN 
 
 (2nd glacial) 
 
 AFTONIAN 
 
 (1st interglacial) 
 
 NEBRASKAN 
 
 (1st glacial) j 
 
 Glaciers from northeast 
 and northwest covered 
 muciL-oX-Siate 
 
 Glaciers from northwest 
 invaded western Illinois 
 

 GEOLOGIC MAP OF ILLINOIS 
 
 showing 
 
 BEDROCK BELOW 
 
 THE GLACIAL DRIFT 
 
 1961 
 
 rVlT ^~ i . i I ■ i ■ * MM. \ * s^ v\\ V\ \\\\V\\\l 
 
 Tertiary 
 (Pliocene omitted) 
 
 Pennsylvania!! 
 (Above No. 6 Coal) 
 
 Pennsylvanian 
 (Below No. 6 Coal) 
 
 m 
 
 Mississippian 
 (Middle and Lower) 
 
 Silurian and Devonian 
 
 ILLINOIS STATE GEOLOGICAL SURVEY. URBANA 
 
 (33307-10M- 10-66)