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 STOCK No. 152% 
 
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State of Illinois, Department 
 
 of Registration and Education 
 
 STATE GEOLOGICAL SURVEY, URBANA 
 
 JOHN C. FRYE, Chief 
 
 EARTH SCIENCE FIELD TRIP 
 
 ALEXANDER COUNTY 
 
 THEBES AND JONESBORO QUADRANGLES 
 
 Leader 
 
 GEORGE M. WILSON 
 
 ILLINOIS STATE GEOLOGICAL SURVEY, URBANA 
 
 October 20, 1956 
 
 GUIDE LEAFLET NO. 56F 
 
 HOST: THEBES 4UGH~SCfi©QL 
 
 
THEBES FIELD TRIP 
 October 20, 1956 
 
 Dis- Mile- 
 tance age 
 
 0.0 0.0 Thebes High School. Align the cars headed south. 
 
 The Thebes area is especially interesting to the geologist because of 
 the extremely interesting series of events that one may unfold. No 
 Pleistocene glacier reached as far south as Thebes, although it did 
 reach the north line of Union County, some forty miles away. There 
 are, however, Pleistocene deposits in this region. We recognize de- 
 posits of sand, gravel, and loess, all thought to be of Wisconsin age. 
 Deposits of pre-Illinoian loess are a short distance away. The loess 
 is relatively fine grained silt that has been picked up from the valley 
 flats and deposited on the hills. 
 
 Study of the map of the Thebes region is especially interesting, f$r 
 there are vast valleys in which small streams flow and a small valley 
 in which the Mississippi flows. It is thought that the small valley 
 or gorge cut south of Gale and extending to Fayville was formed during 
 the time of the Kankakee Torrent, or the Cory substage. During this 
 time the flow of water greatly increased and the flood waters hreached 
 the low ridge between Gale and Fayville. The quantity of water, velo- 
 city and the tools in sand and gravel cut the new channel, thus the 
 channel, which had earlier developed north and west of Gale, was 
 abandoned. 
 
 Finally the flood waters subsided, and great flats resulted in the 
 former river valley. The winds blowing across the valley picked up 
 the fine silt and encountering the high river bluff, dropped its load 
 thicker close to the rivers. This loess is to be found in all of 
 southern Illinois. In this area it is as much as 35 feet thick. 
 
 For the geologist another reason for interest in these rocks is that 
 there are numerous unconformities. An unconformity exists when there 
 is a break in the continuity of rock. An unconformity is a surface 
 of erosion or nondeposition separating younger strata from older. 
 (See illustrations.) There were numerous times that the marine seas 
 covered this region, the lands rose and were subjected to erosion, 
 to be submerged later in the seas, thus there are breaks in the geo- 
 logic column. 
 
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 in 2012 with funding from 
 
 University of Illinois Urbana-Champaign 
 
 http://archive.org/details/earthsciencefiel1956illi 
 
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 The greatest break in the continuity of sediments or unconformity is 
 between the upper Ordovician and the Cretaceous. In this area we 
 have no information and no rock to represent 200 million years. 
 
 In the Illinois coal fields to the north during Mississippian and 
 Pennsylvanian time alone there were at least 3000 feet of sediments 
 preserved. We have reason to believe that these rocks also covered 
 this area but the process of erosion has carried them away. 
 
 Turn right. Shift into Second. Hill. 
 
 Stop. Turn left (west) . 
 
 Slow. Turn left. 
 
 STOP 1 . Thebes Sandstone 
 
 This sandstone is thought to be a lenticular body in the Upper Ordo- 
 vician and corresponds to the Maquoketa shale in the northern portion 
 of the State. The Thebes sandstone varies in thickness, but reaches 
 as much as 100 feet. This fine grained sandstone diminishes in thick- 
 ness and disappears completely, wedging into shale in a relatively 
 short distance. Occasionally marine fossils are found in this sand. 
 
 The Ordovician section in the Thebes area is as follows; 
 
 Thickness 
 Feet 
 
 Thebes sandstone 75-100 
 
 Fernvale limestone 3 
 
 Kimmswick limestone 80 plus 
 
 Details on the Thebes sandstone are as follows: 
 
 Sandstone, silty, shaly, well but thinly laminated 
 Shale, medium gray, silty, with sandstone stringers 
 Sandstone, light gray, fine 
 
 10 
 
 6 
 
 15 
 
 0.8 
 
 l.k STOP 2. 
 
 The Kimmswick limestone is the oldest formation outcropping in southern 
 Illinois, and corresponds with the Galena of the lead-zinc district of 
 
northern Illinois. In this area it is exposed on the crest of the 
 Thebes anticline. An anticline is an arch of rock in which the beds 
 or layers dip in opposite directions at the crest. 
 
 The Kimmswick limestone is coarsely crystalline, and of organic origin. 
 Fossils such a6 the "sunflower corals" or Receptaculit«s, trilobites, 
 bryozoa, corali, and brachiopods are common in this formation. 
 
 Rock of this texture, which can be easily polished, is a potential 
 source for a commercial marble operation. The subsurface equivalent 
 of the Kimmswick has produced oil in several oil pools in Illinois 
 and represents the deepest producing zone in Illinois. 
 
 0.7 2,1 Slow. Rough bridge. 
 
 Orchard Creek shale outcrops in the stream at the mouth of Rock Springs 
 Hollow. 
 
 0,1 2.2 Slow, turn left into Rock Springs Hollow. 
 
 0.1 2.3 STOP j . Silwian limestone - Girardeau formation. 
 
 This limestone %» near tbe base of the Silurian system of rocks. 
 The limestone is characterized by discontinuous layers of thin-bedded 
 limestone with shale partings. It is blup.-gray, fine, brittle and 
 sparsely fossiliferous, although occasionally many fossils are found 
 locally In shale partings. This formation has been called Ordovician 
 and Silurian, but on the fossil evidence and the angular unconformity 
 between the Girardeau and Sexton Creek, It is referred to the Si* 
 lurian system. The Girardeau here is at least 30 feet thick. 
 
 Above the railroad bridge and only a short distance away, is a much 
 younger series of rocks which are of considerable interest. 
 
 The sequence is as follows: Thickness 
 
 Pleistocene Series 
 
 Loess, humic loess soil 2 
 
 Loess, light tan to gray . h 
 
 Loess, brown with tan chert pebbles in the lower 
 portion and with loess concretions or "loess kind- 
 
 chen" 5 
 
 Tertiary System 
 Pliocene Series 
 
 Lafayette formation 
 
 Limonitic conglomerate 1-3 
 
 Clay, red, sandy 2 
 
 Shale, gray and tan, micaceous, moderately well 
 
 bedded 2 
 
 Sand, partially cemented, red, limonitic 3 
 
 Siltstone, fine, light gray, with irregular lenses 
 
 of chert pebble conglomerate 4-12 
 
 Cretaceous System 
 
 Clay, light gray, almost white, micaceous 15 
 
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 J . ■ !■ ■ 
 
 I' 
 
Over much of southern Illinois there are Tertiary gravel deposits as 
 well as Cretaceous clay deposits. Many of the pebbles in the gravel 
 have an outer layer of iron oxide or limonite. An occasional excellent 
 agate specimen may be found. An unconformity of considerable magnitude 
 between the Cretaceous and the underlying Silurian is evident. 
 All of the Devonian, Mississippian, and Pennsylvanian are missing 
 here. There are no known sediments of Permian, Traissic, or Jurassic 
 age in Illinois. Easily 1+000 feet of rock are missing in this interval. 
 
 0.6 2.9 STOP k . 
 
 In the bed of the stream are many chert and agate pebbles, with an 
 occasional Cretaceous fossilized wood fragment. The chert and agate 
 is derived from the erosion of the Lafayette gravels. 
 
 Also in the bed of the stream you will note the olive green to light 
 gray limestone, with an occasional red mass. This is the lowermost 
 Bainbridge limestone of Silurian age. 
 
 0.9 3-7 STOP 5 . Bainbridge limestone. 
 
 The Bainbridge of southern Illinois is a mottled light gray and red 
 stone, which is easily recognized. In this outcrop it is especially 
 red, shaley, and impure, while in the immediate area it is a relatively 
 pure limestone. Fossils are common, especially cephalopods. 
 
 The relationship between the Silurian Bainbridge and the overlying 
 Devonian Bailey is not readily found in this area. 
 
 Note the terraces on the right about 15 feet above the road at 
 approximately kGO feet elevation. 
 
 Slow, turn left (north) . 
 
 Note terraces on the right and left. 
 
 Stop. Danger. Enter Route 3 with caution. Turn right. 
 Note the erosion in the loess covered hills. 
 
 5.1 Note the red Bainbridge limestone in the stream on the right. 
 
 Note the erosion in loess. 
 
 6.8 Note the erosion in the loess covered hills on the left. 
 
 STOF 6 . LUNCH . The Olive Branch School. 
 
 Discussion of the geology thus far seen today and a pre-view of the 
 
 afternoon. 
 
 0.2 8.8 STOP 6k . 
 
 The Devonian limestone (Bailey formation) is cherty, siliceous, but 
 relatively unaltered. The limestone is medium gray, dense and sparsely 
 fossiliferous. More or less continuous bands or beds of chert are 
 common in this formation. 
 
 0.5 
 
 k.2 
 
 o.k 
 
 k.6 
 
 0.3 
 
 k.9 
 
 0.2 
 
 5.1 
 
 0.1 
 
 5.2 
 
 1.6 
 
 6.8 
 
 1.8 
 
 8.6 
 
0.1 8.9 Slow, turn left (northeast). 
 
 0.8 9.7 STOP 7. Bailey formation. 
 
 Here the siliceous, cherty Bailey limestone has been altered to chert 
 and tripoli. Perhaps there has been replacement of the limestone, 
 but it is evident that there has been a reduction in the thickness of 
 the formation. The white powdery material is called tripoli. This 
 material, which is a micro-crystalline quartz was derived from exten- 
 sive weathering of siliceous limestone. The mechanics of this pro- 
 cedure is not understood. 
 
 The section here is as follows: Thickness 
 
 Feet 
 
 Chert, stained red, nodular 15-20 
 
 Chert and tripoli, chert nodules are surrounded 
 by the finely divided tripoli 70 
 
 Slow at Y at Sandy Creek Church, turn right. 
 
 Cut in Grassy Knob chert. In this cut variations in the degree of 
 leaching are evident, for in some places the bedding is preserved, 
 while in others the bedding planes are distorted or lost. 
 
 Slow, turn left. 
 
 Note abandoned silica pit on the left, turn right. 
 
 Slow, caution, turn left (north). 
 
 View of large silica and chert pit dead ahead. 
 
 Slow, turn right. 
 
 STOP 8 . 
 
 The section here is as follows: Thickness 
 
 Feet 
 Pleistocene Series 
 Wisconsin stage 
 
 Loess, buff 10 
 
 Devonian System 
 
 Dutch Creek sandstone, in part altered to quartzite, 
 
 medium to coarse, fossiliferous 0-10 plus 
 
 Clear Creek chert, fossiliferous 30-50 
 
 The percolating waters through time have removed the calcareous cement 
 from the sandstone and removed the lime from the Clear Creek formation 
 so that only the casts and molds remain. A rather wide variety of 
 fossils such as brachiopods, trilobites, corals, gastropods, and 
 pelecypods are to be found. 
 
 0.3 19.8 Stop, turn left on Route 127 . 
 
 3.8 
 
 13.5 
 
 0.7 
 
 1^.2 
 
 0.7 
 
 U.9 
 
 1.1 
 
 16.0 
 
 0.9 
 
 16.9 
 
 0.6 
 
 17.5 
 
 1.6 
 
 19.1 
 
 0.4 
 
 19.5 
 
1.8 21.6 Note the Silica mill on the left, where ganister and tripoli are 
 
 prepared for the market. Ganister is a term applied to a southern 
 Illinois high silica material, which is loosely consolidated and 
 readily disintegrates into irregular particles of an inch or less in 
 size. 
 
 0.5 22.1 STOP 9 . Mississippian System - Osage Group. 
 
 Hartline formation, when unaltered is largely an impure cherty lime- 
 stone, is here a chert and ganister. The formation unconformably 
 overlies the Springville shale. The relations of the overlying Lower 
 Mississippian group of formations including the Burlington, Keokuk, 
 Warsaw, and Salem are not clear. It is thought that the Hartline 
 becomes less cherty to the north. The red earth or red cherty residum 
 is characteristic of the Hartline in this area. The conditions that 
 caused the alteration of the limestones and shales to alter to cherts 
 and tripoli in selective regions is not known. The same processes 
 selectively altered sandstones to quartzites. Only a few miles north 
 on Mill Creek, limestone sufficiently free of impurities is quarried 
 for building stone purposes. 
 
 0.2 22.2 STOP 10 . 
 
 The section here is as follows: Thickness 
 
 Feet 
 Pleistocene Series 
 Wisconsin stage 
 
 Loess, buff to tan 10 
 
 Silt, with chert pebbles K 
 
 Cobbles and guwdlwith sand and silt ^ 
 
 Tertiary System 
 Pliocene Series 
 
 Lafayette formation 
 
 Coarse gravel with gravelly clay filling, pebbles 
 polished, some coated with limonite ....... 5 
 
 Pre -Lafayette (?) 
 
 Gravel, coarse, cherty, pebbles unpolished .... 10 
 
 The deposit here is a terrace remnant at h60 feet elevation. The 
 present valley level is 375 feet. The pebbles in this deposit are 
 largely chert, and some of them have a rather high polish, others a 
 limonite coating. The lower portion of the outcrop may represent an 
 age slightly older than Lafayette. 
 
 SEE YOU NEXT SPRING 
 
Time Table of Pleistocene Glaciation 
 (after M. M. Leighton and H. B. Willman, 1950) 
 
 Stages 
 
 tSub-stages | Nature of Deposits 
 
 Special Features 
 
 I Soil, infant to youthful pro- h 
 file of weathering, lake and l ! 
 river deposits, dunes, peat. 
 
 Late 
 
 Mankato 
 
 Early 
 
 Fluvial deposition - 
 Mississippi, Illinois, and 
 Ohio river valleys; dune 
 sand, some loess deposits 
 along Mississippi River 
 Valley; and deposits in Lake 
 Chicago. 
 
 I Lake Agassiz Torrent 
 j eroded Late Mankato 
 | deposits 
 
 j Lake Duluth Torrent 
 i eroded Early Mankato 
 deposits 
 
 !; Forest bed, Two Creeks, 
 ! Wisconsin 
 
 Wisconsin JCary 
 (Ktb glacial! 
 
 Drift, loess, dunes, beginning' Kankakee and Lake Maumee 
 of deposits in Lake Chicago Torrents 
 
 Tazewell 
 
 Drift, loess, dunes, lake 
 deposits. 
 
 Iowan 
 
 Formdale 
 (Pro-Wis.) 
 
 I Fox River Torrent 
 Westward diversion of 
 Mississippi River into 
 Iowa by Tazewell ice 
 lobe 
 
 Drift, loess, dunes 
 
 Loess (in advance of glacia- 
 tion) 
 
 Sangamon 
 
 (3rd interglacial) 
 
 Soil, mature profile of weath- 
 ering, alluvium, peat 
 
 Buffalo &a?t 
 
 i 
 
 'Jacksonville 
 
 Illinoian Payson 
 (3rd glacial) (terminal) 
 
 Love land 
 (Pro-Ill.) 
 
 Yarmouth 
 
 (2nd interglacial) 
 
 Soil, mature profile of weath- 
 ering, alluvium, peat. 
 
 Kansan 
 
 (2nd glacial) 
 
 Drift 
 Loess 
 
 Aftonian I 
 
 (1st interglacial) 
 
 Soil, mature profile of weath- 
 ering, alluvium, peat. 
 
 Nebraskan 
 (1st glacial) 
 
 Drift 
 

 
 GENERALIZED GEOLOGIC COLUMN 
 
 FOR THE CAIRO AREA 
 
 Prepared by the Illinois State Geological Survey 
 
 ERAS 
 
 PERIODS 
 
 EPOCHS 1 FORMATIONS 
 
 Cenozoic 
 
 Age of Mammals 
 
 Quaternary 
 
 Pleistocene 
 
 Loess and alluvium of several 
 glacial stages 
 
 Tertiary 
 
 Pliocene 
 
 Lafayette gravels 
 
 Miocene 
 
 Not present in Illinois 
 
 Oligocene 
 
 Not present in Illinois 
 
 Eocene 
 
 Wilcox sand and clay 
 
 Paleocene 
 
 Porters Creek clay and 
 Clayton greensand 
 
 Mesozoic 
 
 Age of 
 Reptiles 
 
 Cretaceous 
 
 
 McNairy sands and clays 
 
 Jurassic 
 
 
 Not present in Illinois 
 
 Triassic 
 
 
 Not present in Illinois 
 
 
 CO 
 
 Permian 
 
 
 Not present in Illinois 
 
 o 
 
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 N 
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 rH 
 
 d 
 to 
 
 d 
 
 •H 
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 Pennsylvanian 
 
 Xi to 
 
 «h a 
 o w 
 
 ' Mississippian 
 
 to a 
 
 <; d 
 
 CO 
 Q> 
 
 £1 
 CO 
 
 •H 
 
 to 
 
 O 
 
 o 
 bO 
 
 < 
 
 Devonian 
 
 Chester 
 
 Iowa 
 
 Meramec group 
 Osage group 
 
 Not present in Thebes area 
 
 Not present in Thebes area 
 
 Warsaw-Salem limestone 
 Burlington-Keokuk limestone 
 Hartline chert (chert & ganister) 
 
 Kinderhook group Springville shale 
 
 Upper Devonian 
 Middle Devonian 
 
 Erian group 
 
 Ulster ian group 
 
 Lower Devonian 
 Criskanian group 
 Helderbergian 
 group 
 
 CO 
 
 <D 
 
 ■p 
 
 d 
 u 
 & 
 
 CD 
 •P 
 
 JH 
 
 0) 
 
 o 
 
 j Silurian 
 
 Ordovician 
 
 Niagaran 
 Alexandrian 
 
 Cincinnatian 
 Mohawkian 
 
 Cambrian 
 
 Proterozoic 
 Archeozoic 
 
 1 \ Referred to as "Pre -Cambrian" 
 
 J 
 
 Not present in Thebes area 
 
 Dutch Creek sandstone 
 Clear Creek chert (thick re- 
 sidual chert) 
 
 Bailey limestone and chert (re- 
 sidual chert & tripoli) 
 
 Bainbridge limestone 
 Sexton Creek limestone & shale 
 Edgewood limestone (not seen) 
 Girardeau limestone 
 Orchard Creek shale (and impure 
 limestone) 
 
 Thebes sandstone & shale 
 Fernvale limestone 
 Ximmswick limestone (thick pure 
 limestone) 
 
 Deeply buried in Thebes area 
 
 Deeply buried in Thebes area 
 
 4- 
 
TILL PLAINS SECTION, 
 
 GREAT LAKE 
 
 SECTION 
 
 CENTRAL 
 LOWLAND 
 PROVINCE 
 
 OZARK 
 
 PLATEAUS 
 
 PROVINCE 
 
 ENTRAL 
 
 LOWLAND 
 
 PROVINCE 
 
 INTERIOR 
 LOW 
 
 PLATEAUS 
 PROVINCE 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 COASTAL PLAIN 
 PROVINCE 
 
 PHYSIOGRAPHIC DIVISIONS OF ILLINOIS 
 
 (Reprinted from Report of Investigations No. 129, Physiographic Divisions of Illinois, 
 by M. M. Leighton, George E. Ekblaw, and Leland Horberg) 
 
 ' (7132B1 
 
Plate 
 
 COMMON TYPES of ILLINOIS FOSSILS 
 
 GRAPTOLITE 
 
 Lithostrotion 
 
 CORALS 
 
 Honeycomb coral 
 
 CRINOID 
 
 Sto&#j$», 
 
 PENTREMITE 
 
 Fenestella 
 
 Archimedes 
 
 Branching 
 
 BRYOZOA 
 
 Lingula Orbiculoidea 
 
 Spiriferoid 
 
 Productoid 
 
 Pentameroid 
 
 BRACHIOPODS 
 
Plate 2 
 
 Common Types of Illinois fossils 
 
 "Clam" "Scallop" 
 
 PELECYPODS 
 
 Coiled cone 
 (Nautilus) 
 
 Straight cone 
 
 CEPHALOPODS 
 
 High- spired 
 
 Bumastus 
 
 Low - spired 
 
 Flat - spired 
 GASTROPODS 
 
 Calymene 
 (coiled ) 
 
 OSTRACODS 
 (greatly enlarged) 
 
 Calymene 
 (flat) 
 
 TRILOBITES 
 
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