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STATE OF ILLINOIS 
 
 DEPARTMENT OF REGISTRATION AND EDUCATION 
 
 STATE GEOLOGICAL SURVEY DIVISION 
 
 Morris M, Leighton, Chief 
 
 HARRISBURG AREA 
 
 Harrisburg and Brownfield 
 Quadrangles 
 
 Guide Leaflet 51-A 
 
 by 
 
 Gilbert 0, Raasch 
 
 Urbana, Illinois 
 April 7, 1951 
 
 SN 
 
 & 
 
 
PART I. ITINERARY 
 
 0,0 Caravan assembles headed east on North side of Harrisburg Township High 
 School* 
 
 0.0 Turn right (S). 
 
 0.4 Turn left (E). 
 
 0.7 STOP 210. 1. Brick Works Office. 
 
 Red brick and tile are being made here from Pennsylvanian ("Coal 
 Period") shale that lies above the Herrin (No. 6) Coal Bed, 
 
 0.7 Resume route; turn right through plant yard. 
 
 0,9 Turn left on road way and cross R.R. 
 
 1.0 Stop Sign, Cross Route No. 45 and continue east. 
 
 1.3 Stop Sign. Turn right (S) on Route No. 34. 
 1.6 Enter Pankeyville. 
 
 2.2 Turn left (E) on Ingram Hill Road. 
 
 2.4 STOP NO, 2. Strip Coal Mine. 
 
 Mining operations here were in the Herrin (No. 6) Coal. As indicated 
 in the debris of the strip piles, several inches of black carbonaceous 
 shale overlay the coal and was followed by gray cap rock limestone inter- 
 lensed with gray marine shale. Above this and under alluvial deposits of 
 Pleistocene (Glacial Period) Age, was a varying thickness of gray, silty 
 non-marine shale, as was seen in the brick-works clay pit (Stop No. l). 
 Below the coal was a gray, non-stratified underclay. 
 
 The black slate here yielded no fossils but commonly rock of this type 
 contains fossils indicating an environment in which certain special forms 
 of marine animals were able to live. In general the habitat may have been 
 in the nature of brackish coastal lagoons often with the stagnant poison- 
 ous bottom waters. 
 
 The limestone and marine shale above the black "slate" was deposited 
 under conditions of freely circulating sea waters, so that such typically 
 marine animals as crinoids ('sea lilies"), bryozoa, brachiopods, and even 
 small corals were able to live here. 
 
 The marine shale and limestone grades upward into shales and sandy 
 shales in which no marine fossils are present and only the remains of land 
 plants are rarely found. Evidently sediments washed from the lands of the 
 time filled the shallow sea and caused a retreat of the coast line. 
 
 The coals themselves are believed to have been deposited in great 
 fresh water swamps of a low coastal plain, and the underclay is thought by 
 many to have been an ancient soil in which the coal forests grew. 
 
-2- 
 
 Conditions changed frequently and were many times repeated during the 
 millions of years that went to make up the Goal Period (Pennsylvanian 
 Period). Although most of the 2000 feet or more of coal bearing strata 
 are made up of non-marine shales and sandstones, thin limestones, marine 
 shales, coal beds, and underclays, occur again and again in the succession 
 of sedimentary layers. 
 
 0.0 2.4 Resume route - continuing ahead. 
 
 0.3 2.7 Turn right (N) on road to old mine, loop right, and retrace course to 
 Route No. 34. 
 
 0.8 3.5 Stop. Turn left (S) on No. 34. 
 
 0.9 4.4 STOP NO. 3. View southeast to Shawneetown "Fault Scarp". 
 
 From this point we look southeast across an ancient lake flat (see 
 Stop 4) to the high range of hills running from Williams Hill on the 
 right through Bald Knob and Cave Hill and eastward to the Wildcat Hills 
 and beyond. 
 
 Most of Illinois, very flat on the surface is a spoon-shaped basin so 
 far as the attitude of the rock layers is concerned. The steep part of 
 the spoon is at its south end and here layers come up out of the basin to 
 crop out at the surface. Coal No. 6 for example lies below sea level in 
 the northern part of Saline County and rises steeply to come to the sur- 
 face south of Harrisburg (as at Stop No. 2). 
 
 Intense movements of the earth's crust in the distant geologic past 
 caused the southeast tip of Illinois to move northwestward against the 
 south end of the coal basin. This segment of the crust moved along a rup- 
 ture or fault (Shawneetown Fault) which lies today at the base of the 
 range of hills. The fault movement brought to the surface hard massive 
 sandstones of early Pennsylvanian age, of which the hills are made. 
 
 1.9 6,3 STOP NO, 4. Park along highway. 
 
 Road here descends low bluff to Saline River flats. The river here 
 does not flow in a flood plain of its own making. The flats are underlain 
 by clay and silt deposited in the bed of an ancient lake. The lake 
 existed late in the Ice Age and came about as follows: 
 
 The Mississippi River was carrying a great deal of water and sediment 
 in the form of mud, sand, and gravel washed out from a melting glacier 
 that stood in the upper Great Lakes and Red River Valley. The Ohio River, 
 on the other hand, was not carrying glacial melt waters. 
 
 The Mississippi built up its flood plain to a great height and thus 
 dammed back the tributary Ohio River, which virtually became a long, 
 narrow lake, with arms that extended up the tributaries, such as the 
 Saline River Valley. Mud and sand that washed into the lake eventually 
 filled it and buried the bases of many of the hills, like that lying a 
 half mile to the southeast. The old lake flat lies 360 to 370 feet above 
 present sea level. 
 
 Much earlier in the Ice Age, the Illinoian glacier just about reached 
 the point where we stand. This can be determined by the distribution of 
 boulders of rock found today only in the far norhtern regions from which 
 the glaciers came. South of here, in the Shawnee Hills, the region never 
 has been glaciated, and no such boulders occur. 
 
-3- 
 1..0 7.3 South Fork SALINE RIVER. 
 0.7 8.0 Enter Mitchells villa, 
 0*4 8.4 Forks? take right fork, leaving pavement. 
 
 1.6 10«0 For next 0.4 mile road ascends steep grade through cuts in sandstone of 
 
 Pennsylvanian, Tradewater age. 
 
 0.4 10.4 STOP NO. 5. 
 
 As we go downward in the Pennsylvanian strata below the main produc- 
 tive .coal measures, the strata become increasingly sandy. The most pro- 
 ductive of the coal measures are called the Carbondale Group. Under this 
 lies the much sandier Trad ©water Group, hundreds of feet thick. 
 
 The sandstone in the highway cut is a part of this Tradewater Group. 
 It can be seen to lie in parallel strata sloping gently northward, as the 
 beds are here sloping downward toward the center of the Illinois Coal 
 Basin. Near the summit of the grade, the strata are broken and south 
 across the small gully they can be seen to slope steeply southward. The 
 draw itself is the site of a fault zone, here a minor rupture of the 
 earth' s crust, where a block to the south settled downward at some time 
 in the distant past. The rock was highly shattered close to the fault and 
 thus easily eroded to form the small gully. The strata south of the gully 
 were dragged from a nearly horizontal position as the southern block 
 dropped downward. 
 
 0.9 11*3 Cross bridge over tributary of Battle Ford. Pennsylvanian Sandstone in 
 cut north of bridge shows excellent vertical joint planes (Murray Bluff 
 Sandstone). 
 
 1.7 13.0 CEDAR BLUFF CHURCH. 
 
 0..2 13*2 Road east to Williams Hill and Herod. The attractive skyline drive 
 
 affords fine views of the Shawnee Hill country and the plains to north. 
 Williams Hill, over 1060 feet high, is the highest point in southern 
 Illinois. 
 
 Sandstone ledges in road cut are of Pennsylvanian, Tradewater age 
 (Delwood) and show excellent cross-bedding. 
 
 0.5 13.7 Turn right (W) on road to McCormick Tower and Belle Smith Spring. 
 
 2.8 16,5 STOP NO. 6. Flat Rock School, 
 
 The road has been following a high divide which is the edge of a north- 
 facing cliff or escarpment. This escarpment is made by thick layers of 
 Caseyville sandstone which is here brought to the surface as a result of 
 the erosion of a sharp up- fold in the strata. This upfold is called the 
 McCormick anticline, and runs from Cedar Bluff southwest to McCormick, 
 beyond which it passes into a fault. 
 
 The hills to the north are produced by hard strata in the upturned 
 edge of the Illinois Coal Basin. These strata dip north until they lie 
 at a great depth under the plains of the Coal Basin. 
 
.-..■ 
 
 '' 
 
-4- 
 
 Most of the hills to the north rise to heights of between 600 and 700 
 feet. This level was once a continuous rolling plain, called the Lancas- 
 ter or Ozark Peneplain, xvhich had resulted from the erosion of the region 
 down to base level. Then a limited uplift of the entire region enabled 
 the streams to cut down below the level of the old peneplain, and the re- 
 gion was once again dissected into a complex of ridges and valleys, as we 
 see it today» 
 
 The skyline ridge and hill summits to the south are in hard massive 
 sandstone that rose as low hills, about 100 feet above the old peneplain 
 level. Their flat summits, all rising to about the same general level, 
 may be the last remnants of what was once a still higher and still older 
 peneplain. 
 
 2.0 18.5 STOP NO. 7. Descend to Burden Falls. 
 
 The stream descends in about a 40 foot vertical drop over Pennsylvan- 
 ian, Caseyville sandstone where erosion has cut a canyon back one-half 
 mile into the escarpment formed by the McCormick anticline. Numerous 
 quartz pebbles may be seen in the sandstone. Such pebbles are typical of 
 basal Pennsylvanian beds over much of eastern North America. They seem 
 to have been developed on a land surface during the time interval that 
 separated deposition of Mississippian and Pennsylvanian strata in the 
 region. 
 
 0.5 19.0 Road junction south of McCORMICK FIRE JOKER. Turn left (S) along ridge 
 top. 
 
 1.5 20.5 Junction. Turn left (W) on road to Belle Smith Spring. 
 
 1.5 22.0 Forks. Go left to Belle Smith Spring parking area. 
 
 0.7 22.7 LUNCH STOP, Go back up road a short distance to trail that descends 
 bluff to west. 
 
 STOP NO. 8. The samo sandstone seen at Burden Falls is present here. 
 This is the Caseyville sandstone the lowest group or division of the 
 Pennsylvanian strata. At the time this sandstone was being deposited in 
 Illinois, very high mountain ranges were rising along what is now the 
 Atlantic Seaboard. As the mountains rose, erosion tore away the exposed 
 strata and great streams carried the sediments westward across the low 
 country, which it buried under hundreds of feet of sand. 
 
 That this sand was deposited above sea level is indicated by the fact 
 that no marine fossils are found in the Caseyville sandstone but only the 
 remains of land plants, which may either have lived here or floated here 
 from the eastern high lands. In one of the sandstone blocks used to pave 
 the stairway that descends through the narrow rock crevice to the picnic 
 grounds, the impression of an ancient log may be seen. This has leaf 
 scars arranged in parallel rows separated by pleat-like ridges. This in- 
 dicates the tree to have been a Sigillaria, a species of club moss, whose 
 modern relatives stand seldom more than a foot high in our modern forests. 
 
 The gorge of Bay Creek has been eroded back from the Chester Escarp- 
 ment, which we will see at Stop No. 9 and which marks the southern limit 
 of the Pennsylvanian outcrop. It is obvious that large vertical cracks in 
 the massive sandstone have aided the forces of erosion in cutting the 
 
..f 
 
 7 . 3 f'i 
 
gorge and side gullies. Joints differ from faults in that, while the 
 rock is broken, no movement has taken place between the sandstone masses. 
 The development of joints may be compared to the cracking of safety 
 glass. Rock layers, like sheets of glass, are brittle, especially when 
 deeply buried and thus under heavy pressure. A slight twist in the 
 earth's crust will cause the layers to shatter in a pattern of cracks, 
 but the individual pieces (joint blocks) remain in place. 
 
 As the waters of the stream undermine the cliffs, the joint blocks 
 topple into the valley. Rarely a block will be completely worn through 
 in the middle but remain standing as an arch, while a weaker block behind 
 it crumbles av/ay. Thus a "natural bridge" like that south of the picnic 
 ground, is developed. This is one of two natural bridges in Illinois. 
 
 A large fallen block north of the bridge and on the opposite side of 
 the stream has its surface covered with ripple marks, indicating that the 
 sandstone originated as sand deposited in shallow standing water, perhaps 
 a large bayou lake. 
 
 °ome large blocks instead of toppling have slipped sideways av/ay from 
 their original position. This has probably been caused by a slippery 
 shale zone now concealed below the sandstone masses. The existence of 
 springs close to stream level also strongly suggests the presence of a 
 shale stratum. 
 
 Sandstone is very porous and water circulates through it freely; but 
 on reaching the impervious shale, the water moves laterally to come to 
 
 the surface as springs wherever erosion has cut down through the sandstone- 
 shale contact. 
 
 0.0 22.7 Retrace route to junction with Eddyville Road. 
 
 2.2 24.9 Junction with Eddyville road. Turn right (S). 
 
 0.7 25.6 WATKINS FORD over Bay Creek. Ascend steep hill beyond to ridge summit 
 and take left fork, keeping on upland, 
 
 3.5 29.1 STOP. Turn right (S) on Route No. 145. Pennsylvanian (Tradewater) sand- 
 stone exposed in cuts for next mile. 
 
 1.2 30.3 About 5 feet of sandstone on 25 feet of gray shale and sandy shale. 
 
 (Probably Grindstaff sandstone on uppermost shale of the Pounds formations. 
 
 1.7 32.0 Caution. Cross EDDYVILLE blacktop road, 
 
 1.8 33.8 For next mile, road runs close to edge of Chester escarpment, 
 
 1.0 34.8 STOP NO. 9. Long grade descending Chester Escarpment. 
 
 The thick solid sandstono that lies at the base of the Pennsylvanian 
 rests on a series of weaker strata below that are of Mississippi'an, 
 Chester age. The Chester strata therefore, erode rapidly and cliffs or 
 steep ridges are cut back to the protecting basal Pennsylvanian (Casey- 
 ville) sandstone, which forms the cap rock of the escarpment. Only a few 
 feet of Caseyville sandstone remain at this place, at the very top of the 
 cut, above the streak of pale silty sandstone. The Caseyville here is 
 coarse and poorly sorted and has many rounded pebbles of milky quartz. 
 It makes an irregular contact with the rock beneath, cutting down into the 
 underlying layers. There are many pockets of red clay along this line of 
 contact. 
 
" \C 
 
-6- 
 
 Aftor the deposition of the last Mississippian sediments, the region 
 was uplifted to a land area and subjected to erosion. The rocks weathered 
 and soils formed. Only such hard and nearly insoluble rocks as quartg 
 and chert remained on or near the surface. As the land sank again early 
 in Pennsylvanian time, sediments again were deposited over the former 
 upland surfece, and what ever materials had accumulated there were in- 
 corporated in the sediments at the base of the Pennsylvanian* 
 
 The Mississippian layers in the region total near 3000 feet. The 
 lower half is mainly thick formations of marine limestone, with black 
 carbonaceous shale at the base. This "Iowa Group" of strata does not 
 reach the surface in the field trip area. 
 
 The upper division of the Mississippian, the Chester Group, consists 
 of an alternating series of rather thin formations of sandstone and of 
 limestone and shale*, In Chester, as in Pennsylvanian time, there was thus 
 an alternation of marine and non-marine conditions, with this difference. 
 Few if any of the Chester strata seem to have been deposited under land 
 conditions. The non-marine sandstones and shales appear to have been laid 
 down in lakes or estuaries that were partly cut off from the sea and the 
 waters of which were kept fresh by the influx of large streams. The 
 environment may be comparable to that of the present west coast of 
 Florida north of the Everglades, 
 
 Except for the lowest sandstone (Degonia) seen near the base of the 
 long grade, the strata below the base of the Pennsylvanisn here oil be- 
 long to the KinKaid Formation of the Chester Group, At top is about 12 
 feet of sandstone in thin layers without pebbles. The next rock to be 
 seen is varicolored clay shale, which carries a spring line at the upper 
 contact, and is about 40 feet thick. Below this is about 40 feet of sand- 
 stone, above another varicolored clay body, which grades downward into a 
 highly siliceous and chorty, black, brown weathering limestone. The 
 limestone has many fossils, including brachiopods, bryozoa, and gastropods 
 (snails), indicating marine conditions, wnen the rock weathers, the calf 
 cium carbonate leaches away leaving a light weight, spongy rock that is a 
 siliceous skeleton of the originally siliceous limestone. 
 
 Below t\\Q limestone is more clay and shale and finally the top beds of 
 the underlying Degonia sandstone* 
 
 1.0 35,8 Bridge over Hayes Creek. 
 
 0,3 36.1 Cut in dark green KinKaid shale; 
 
 1.1 37.2 Cut in dark green Kinkaid shale, 
 0.5 37*7 "Y M Highway junction; curve left, 
 
 0.5 38.2 Junction with blacktop highway) continue left (S)v 
 
 0*1 38.3 Bridge over Hayes Creek, 
 
 0.1 38.4 GLENDALE, Outcrops of Degonia (Chester) sandstone. Continue ahe^ad (S), 
 
 1.4 39.8 University of Illinois Agricultural "xperiment Station on left. Outcrops 
 in next mile are Chester sandstone. 
 
*\ '■ 
 
-7- 
 
 1.4 41.2 Cross Sugar Loaf Creek, 
 
 0.1 41.3 Road east goes to Lake Glendale. Continue ahead (S). 
 
 1.5 42.8 STOP NO. 10. Park along highway. 
 
 Fault in Chester strata. Most faults are poorly exposed because the 
 shattered strata along the fault zone weather readily, so that a small 
 valley commonly conceals the actual fault. The present locality is ex- 
 ceptional in preserving full details of the faulting. 
 
 The thin bedded sandstone strata standing nearly vertical are the 
 Tar Springs Sandstone, Note the ripple marks, made Then the horizontal 
 layers were being deposited as sand on the floor of a lake or estuary. 
 
 The nearly vertical shale layers west and north of the sandstone 
 strata belong to the Vienna Formation, xvhich normally should lie below 
 the Tar Springs. Notice that the shale beds are not exactly parallel to 
 the sandstone beds (i.e. have a somewhot different "strike"). Also 
 masses of shala have been shoved between sandstone layers indicating 
 there was some horizontal movement along the fault. 
 
 Bands of clay full of sandstone fragments are fault gouge" where the 
 strata were ground up by the faulting. 
 
 On the opposite side of the road, away from the fault, the strata may 
 be seen to dip rather gently; the same is true as one goes northward 
 along the east side of the road and thus farther away from the fault zone. 
 
 This fault is one of many which cut the Illinois-Kentucky fluorspar 
 district into a complicated mosaic of long narrow fault blocks. These 
 faults are not to be confused with the Shawneetown fault farther north 
 (Stop No, 3) which developed at an earlier date. 
 
 The fault mosaic of Pope and Hardin counties is thought to have 
 developed first as the result of the doming of the region, probably be- 
 causo of the intrusion at great depth of a mass of molten magma (igneous 
 rock material, called lava when it comes to the surface). Although such 
 an igneous body has never been reached, many dikes of ignoous rook 
 (poridotite) cut the strata in this region. These dikes are doubtless 
 off-shoots of the main mass. 
 
 After the strata of the region has been shattered by doming, the dome 
 collapsed, and a second period of faulting took place. The collapse may 
 have been duo to a partial withdrawal of the igneous mass. Nevertheless, 
 gaseous and vaporous emanations continued to rise along crevices and 
 especially along some of the fault zones. As the vapors chilled on 
 approaching the siirface the valuable f luorspar-zinc-lead-silvor ores were 
 deposited in the crevices. 
 
 All these events took place some time after the Pennsylvanian and 
 before the Cretaceous period, 
 
 0.5 43.3 Mississippian (Tar Springs) Sandstone, in nearly horizontal layers, 
 
 0.2 43.5 Tar Springs Sandstone layers with southerly dips on shale. 
 
 0.1 43.6 Caution . Pass over Route No. 146; stop sign beyond. Continue ahead (S) 
 on No. 145, 
 

-8- 
 
 2.0 44.6 REUS HAW; Park along pavement and ascond small road loft, to bluff top. 
 
 STOP NO. 11. Cache Valley. 
 
 Wo arc looking south westward down the Valley of the Ohio River. 
 There is no river here today because in the not distant geologic past the 
 Ohio escaped from its own valley and broke over into the valleys of the 
 Cumberland and Tennessee rivers, which it follows today in its course 
 from Bay City to Cairo, to join the Mississippi there. Cache Valley 
 which you sec before you is almost exactly as the river left it, roughly 
 a score of thousands of years ago. 
 
 Cache Valley as we see it today is filled with alluvium deposited 
 there by the Ohio up to the time it abandoned this channel. The valley 
 that the river actually cut down into the hard bedrock is much deeper, 
 down to 175 feet above sea level at Ullin. Thus 165 feet of alluvium 
 partially fills the old valley. The now valley (the valley originally 
 cut by the Tennessee River), although cut in soft coastal plain sediments 
 was not excavated to so great a depth, reaching only to about 250 feet 
 above sea level at Mound City. 
 
 Late in the Ice Age, the valley of the Mississippi was filled to 
 great depth with sand and gravel washed out from the melting glaciers to 
 the north and the valleys of the Ohio and Tennessee filled up to the 
 same level with slack water silt and clay. This equalized the difference 
 in the depths of the original valleys and made it easy for the Ohio to 
 break through a low divide and capture the lower valley of the Tennessee. 
 
 The past was restored briefly in 1937 when during the Great Flood 
 the Ohio rose so high that a part of its waters spilled out through the 
 old Cache Valley. 
 
 0.0 44.6 Continue ahead (S) on No. 145. 
 
 0.1 44.7 Caution - RR Crossing. 
 
 4.7 49,4 Ledges of Chester (Hardinsburg) sandstone dipping steeply because of 
 proximity to a fault. 
 
 0.1 49.5 Horizontal ledges of Hardinsburg sandstone. 
 
 1.1 50.6 STOP NO. 12. Park along highway on hill near junction with Round Knob 
 
 Road (right). 
 
 Gravel Pit in LaFayette Gravel on Cretaceous sand. 
 
 In a general way, Cache Valley forms the boundary between the Shawnee 
 Hills region of older, solidified, disturbed and faulted rocks to the 
 north and younger, unconsolidated, nearly flat lying rocks of the Gulf 
 Coastal Plain to the south. The unconsolidated rocks in the [.ravel pit 
 belong to the Gulf Coastal Plain region. Here at the north edge of the 
 plain, the region has been dissected into low hills and gullies. 
 
 The gravel in the pit consists of rocks, mainly chert, that have boon 
 washed off the high lands to the north, as is indicated by the common 
 prcsenco of Mississippian fossils in the chert. Although the deposits 
 wore evidently laid down by streams, two features of these "LaFayette 
 Gravels" regain unexplained. They do not so much occur in channels as in 
 widespread blanket deposits, and the pebbles are always highly polished. 
 The gravels were laid down before the Ice Age (Pleistocene) but after the 
 withdrawal of the Tertiary Sea in Eocene time. 
 
-9- 
 
 Tho uppor couple feet of the gravel is deeply v;eathered to a residual 
 clay, with only a few pebbles remaining. This indicates long exposure 
 under upland conditions. Above the cl?y are two or three feet of loess, 
 "dust" that settled here during the Ice Ago as the frigid winds swept up 
 the fine sediments from the alluvial flats of the Mississippi and the 
 Ohio-Cache to the West. The upper foot of loess has been altered to a 
 lean forest soil. 
 
 At the south end of the pit, loose red sand is exposed below the 
 gravel. This sand, of Cretaceous age, is much older than the gravel and 
 was deposited in the Gulf Embayment which extended this far north in 
 Cretaceous rnd Eocene time. Today the sediments of the Mississippi and 
 its tributaries have filled this embayment as far as the present delta 
 below New Orleans. 
 
 Thus the line between the Cretaceous sand below (deposited in the days 
 of the dinosaurs) and the late Tertiary gravels above represents a great 
 span of geologic time. Such a line geologists call a "hiatus," commonly 
 also an "unconformity." 
 
 End of Trip - Bon Voyage, 
 
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GENERALIZED GEOLOGIC COLUT5N 
 
 HARRIS BURG AREA 
 
 Prepared by the Illinois State Geological Survey 
 
 ERAS 
 
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 PERIODS 
 
 EPOCHS 
 
 
 FORMATIONS 
 
 Quaternary 
 
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 —4 
 
 Pleistocene 
 
 Pliocene 
 
 o 
 
 b.0 i. 
 
 \ Tertiary 
 
 | Miocene 
 ; Oligocene 
 
 Eocene 
 
 Paloocene 
 
 Cretaceous 
 
 TB~~i 
 
 o 
 
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 ft 
 
 O 
 P-1 
 
 <^ i Jurassic 
 o 
 
 
 Cache Valley; Stop 11 
 Lake Deposits; Stop 4 
 
 ! Illinoian Till; Stop 4 
 
 j Loess; Stop 12 
 
 La Fayotte Gravel; Stop 12. 
 
 Not present in field trip 
 ! area. 
 
 ! Stop 12. 
 
 j 
 
 Not present in Illinois 
 
 
 Triassic 
 
 | Hot present in Illinois 
 
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 •H 
 
 o 
 
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 03 
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 j Permian 
 
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 5 £ I Pennsylvanian 
 
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 *3 ^ j Mississippian 
 
 \.. 
 
 
 Not present in Illinois. 
 
 McLe a ns b oro_ 
 
 Carbondale .. 
 
 Tradewater 
 
 Beds above Conl 6; Stops 15:2 
 
 j 
 
 j No. 6 Coal - Stop 2 
 
 J Stop 5 1 _ _ 
 
 Qase yv ille j Stops 1, 8, 9, 
 
 ™¥Tt """ 
 
 Ob I 
 
 ^jH ] Devonian 
 
 Chester Group 
 L J owa Gro up __ 
 
 to ! Silurian 
 
 © i 
 
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 ^P"£ lOrdovician 
 
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 Stops 9, 10. 
 
 Deeply buried in field trip 
 ' area 
 
 Deeply buried in field trip 
 
 j area 
 
 i Deeply buried in field trip 
 area 
 
 i 
 
 i 
 
 
 Cambrian 
 
 Deeply buried in field trip 
 area 
 
 Pre-Cambrian 
 
 j Deeply buried in field trip 
 area 
 

-10- 
 
 PART II. GEOLOGIC HISTORY OF HARRIS3URG- METROPOLIS AREA 
 
 In going from Harrisburg south to Metropolis, the route begins in the 
 Illinois Coal Basin, crosses the Shawnee Hills, and terminates on the Gulf 
 Coastal Plain. Each of these three geological districts has different charac- 
 teristics and a different history. 
 
 DEEPLY BURIED FORMATIONS. 
 
 The oldest rock to crop out in the area, strata of Mississippian Age, 
 comes to the surface in the Shawnee Hills. But much older strata lie buried 
 below the Mississippian and younger rocks. This we kno\v from the fact that, 
 as we go westward older and older strata come to the surface, until in the St. 
 Francis Mountains of Missouri there is exposed the granite foundation over whioh 
 all of the stratified bedrock layers of the Illinois crust have been laid down. 
 The granite foundation or basement is by no means the original crust of the 
 earth, but consists of rock so old and so distrubed and altered by ancient dis- 
 turbances that it has lost its bedded character and been cut by injections of 
 molten rock from deep in the crust. Before the ancient Paleozoic seas came to 
 Illinois, this basement was worn to a nearly flat plane by erosion acting 
 through an immense span of time. 
 
 The layered bed rock in Illinois, from the Cambrian Period through the 
 Devonian, was deposited as sheet upon sheet of sediment, largely over the floors 
 of ancient seas that inundated the interior of the continent. These sheets of 
 sand, clay, and lime mud in time hardened into the sandstone, shale, and lime- 
 stone bedrock, which encloses the fossil remains of the animals that inhabited 
 the ancient seas. Deep wells in the region today penetrate deep into these 
 ancient strata. 
 
 MISSISSIPPIAN SYSTEM. 
 
 The Mississippian Sea also spread widely into what is now the 
 Mississippi Valley, and in its early stages deposited many thick limestones, 
 probably in rather deep waters. Later, indications are that the crust in this 
 region became somewhat unstable with perhaps an alternating rising and sinking; 
 so that at times the bulk of the land lay below sea level, at other times bars 
 and deltas built out from the coastline and fresh-water or brackish bays, 
 lagoons,, and estuaries were developed. Finally there was a general warping of 
 the earth's crust and a general rise of the land out of the sea, followed by 
 erosion of the higher areas. 
 
 PENNSYLVANIA^ SYSTEM. 
 
 The rising tendency of the North American Continent, which began toward 
 the end of Mississippian time continued more strongly into Pennsylvanian time 
 in the East, as high mountains rose along the Atlantic seaboard. The sediments 
 stripped by erosion in vast quantities from these rapidly rising heights were 
 carried westward by great rivers to the ocean, an arm of which continued to 
 exist in the southwest in the region of Oklahoma and Texas, Thus great masses 
 of sandstone and shale were deposited across the intervening lowlands (including 
 Illinois), which might be compared with the present Amazon Basin at the foot 
 of the towering Andes. 
 
-11- 
 
 As the great mass of sediment accumulated in the lowlands, it tended to 
 depress the underlying earth's crust to a sufficient degree to allow the sea to 
 spread over the lowlands for limited periods. Then an increased dumping of 
 sediment from the highlands x'vould fill the basin and once again shut out the 
 sea. As the periodic sinkings began, there seem to have been stages, before 
 the flooding by the sea, when the region was covered by immense fresh water 
 swamps. These were surrounded and covered by a rank tropical vegetation of 
 ferns, horsetails, and club moss trees, forming dense cane breaks. When the 
 vegetation died it fell into the shallow but sediment-free water and was thus 
 protected from complete decay. These peat-like masses eventually hardened into 
 valuable coal seams. 
 
 The first known amphibians and the earliest of reptiles lurked in these 
 swampy jungles, when the oldest known insects hung in the miasmic air. The 
 Pennsylvanian is the first period in Earth's history in which plants and animals 
 moved from the sea to the land on a large scale, 
 
 POST- PENNSYLVANIAN DISTURBANCES* 
 
 Probably at the close of Permian Time, when the Appalachian Mountains 
 were rising in the East, different segments of the earth's crust in the Illinois 
 region began to move slowly up or down. An area embracing the major part of 
 Illinois slowly sank to produce the rich Illinois coal and oil Basin. The 
 southeast tip of Illinois, on the other hand, along with the adjoining parts of 
 Kentucky rose relatively to an immense stratal dome. As the differential be- 
 tween the dome and the basin became greater and stresses increased, the dome was 
 thrust northwestward, with the resulting formation of the great Shawneetown 
 fault and the weaker McCormick anticline (an upfold, in the nature of an 
 immense crease). The resulting release of pressure (tensional effect) may have 
 permitted the intrusion, deep underground, of an immense mass of molten rock 
 magma (called lava when it reaches the surface). This further expanded the 
 dome in an intricate set of breaks, or faults. Some of the magma rose through 
 these breaks and crevices as high as the Mississippian and Pennsylvanian strata. 
 (Some coal beds have been locally baked by the intense heat of this magma 
 material). These crevice fillings hardened to a dark crystalline rock called 
 peridotite. 
 
 Probably owing to the later withdrawal of part of the molten subter- 
 ranean rock mass, the dome partially collapsed and new fault breaks developed 
 in the strata, as great blocks of the crust wedged downward. Nevertheless, 
 much slowly cooling and solidifying magma must have remained below from which 
 vaporous emanations and boiling waters rose along the crevices to deposit 
 valuable veins of fluorspar- lead-zinc-silver. 
 
 THE ANCIENT GULP OF MEXICO. 
 
 Following the crustal disturbances that took place not long after the 
 Coal Period in Illinois, there followed a long quiescent period during which 
 erosion was busy cutting away the rock strata from the high areas and carrying 
 the debris to the low places as sediments. Thus thousands of feet of Pennsyl- 
 vanian strata, including many millions of tons of coal, were stripped from the 
 Shawnee Hills, where the older Mississippian strata were laid bare. 
 
« ■•'. .-1 
 
-12- 
 
 By this time the interior of North America had assumed the general 
 conformation that it has today. Doubtless an ancestral Mississippi extended 
 through the drainage basin of what are now the valleys of the Missouri, Upper 
 Mississippi, Illinois, and Lake Michigan. The Gulf of Mexico extended north to 
 include the tip of Illinois. By Cretaceous time, the sediments brought down 
 the ancient Mississippi began to fill the upper end of this Gulf of Mexico em- 
 bayment and a coastal plain began to develop. Today the great load of sediment 
 carried by the Mississippi and its (now) r .'estern tributaries have filled this 
 embayment as far as the delta below New Orleans. The process is still continu- 
 ing at a (geologically) rapid rate. 
 
 As erosion leveled the areas of high relief, the region was reduced to a 
 plain of base level, called a peneplain. As the region was moderately uplifted 
 from time to time, above the base level of erosion, the streams would again be 
 able to cut down below the former plain level and carve the country into hills 
 and valleys. But the ridgetops would retain a general level, representing 
 remnants of an older peneplain surface, not yet completely worn away. Thus 
 evidences of former peneplains are still preserved at several different levels 
 in the Shawnee Hills, of \vliich the most prominent, lying close to 700 feet above 
 sea level, belongs to the last, or Salem- Lancaster Peneplain of late Tertiary 
 age. 
 
 This peneplain is characterized in many places by the deposits of highly 
 rounded and shiny surfaced chert gravels, called the LaFayette gravels, which 
 are widely distributed from Louisiana to risconsin. 
 
 THE EFFECTS OF THE ICE AGE. 
 
 Just before the coming of the glaciers to open the Pleistocene Period 
 (ice Age), the region was uplifted several hundred feet and the dissection by 
 streams of the Salem-Lancaster Peneplain surface began. At this time an ances- 
 tral Mississippi River lay to the west but nothing resembling the Ohio River 
 existed. The region of southern Ohio was drained by a series of north-f lowing 
 streams. 
 
 As the glaciers moved down into tho Lake Erie Basin and toward central 
 Ohio, the streams were dammed to form lakes which rose until they spilled west- 
 ward over rocky divides, to form a chain of lakes. As the waters of their out- 
 lets cut gorges through the rocky divides a continuous river eventually developed, 
 which is the present Ohio. How and why the original Ohio Valley across southern 
 Illinois is no longer used is already described in some detail under Stop 11, 
 
 There were four major stages of glaciation during the Ice Age, and only 
 the third of these, the Illinoian got as far south as the Harrisburg Area. Thus 
 the Shawnee Hills were never glaciated. However, as has been described in Part 
 I, the glaciation had indirect effects in the alluviation of the major streams 
 and the filling of tributaries with sediment to a like level, and in the deposi- 
 tion of wind-blown loess over the uplands. The net effect \»;as to enrich the 
 soil over important sections of the region. 
 
 Today, erosion is again in process of cutting down the region to a new 
 base level at some immensely distant future date. 
 
-13- 
 
 Recommended References 
 
 "The Geological Making of Southern Illinois" Stuart Weller. 
 111. State Geol. Survey, Educational Series, Vol. 3. 
 
 "Geology and Oil Possibilities of Extreme Southern Illinois" J. Marvin "Teller. 
 Ill, State Geol, Survey, Report of Investigations, No, 71, 
 
 "Dongola, Vienna, and Brownfield Quadrangles" S. We Her and F, Xrey. 
 111. State Geol. Survey, Report of Investigations, No, 60. 
 
 "Geology of Hardin County'' Stuart We Her et al. 
 111. State Geol, Survey, Bulletin No. 41. 
 (Out of print; available in libraries.) 
 
 "Geology and Mineral Resources of Equal ity-Shavmeetovm Area." 
 111. State Geol. Survey, Bulletin No. 4-7. 
 
 "Bedrock Topography of Illinois" Leland Hbrbere. 
 111. State Geol. Survey, Bulletin No. 73. 
 
 "Coal Resources of District V" (Saline and Gallatin Cos.) G, II. Cady. 
 Ill, Coal Mining Investigations, Vol. 19. 
 
 Earth History Guide Leaflets of Vienna, Cave- in-Rock, and Cairo areas; by 
 Gilbert 0. Raasch 
 
10 
 
 8 
 
 7: 
 
 13"-= 
 
 s 
 
 I I I I 
 
 
 rzi 
 
 Shale, gray, sandy at top ; contains marine fossils and ironstone 
 concretions especially in lower part. 
 
 Limestone ; contains marine fossils. 
 
 Shale, black, hard, laminated ; contains large spheroidal concre- 
 tions ("Niggerheads") and marine fossils. 
 Limestone ; contains marine fossils. 
 
 Shale, gray ; pyritic nodules and ironstone concretions common at 
 base ; plant fossils locally common at base ; marine fossils rare. 
 
 Coal ; locally contains clay or shale partings. 
 
 Underclay, mostly medium to light gray except dark gray at top ; 
 upper part noncalcareous, lower part calcareous. 
 
 Limestone, argillaceous ; occurs in nodules or discontinuous beds ; 
 usually nonfossiliferous. 
 
 Shale, gray, sandy. 
 
 Sandstone, hne-grained, micaceous, and siltstone, argillaceous; 
 variable from massive to thin-bedded ; usually with an uneven 
 lower surface. 
 
 AN IDEALLY COMPLETE CYCLOTHEM 
 
 (Reprinted from Fig. 42, Bulletin No. 66, Geology and Mineral Resources of the Marseilles. 
 Ottawa, and Streator Quadrangles, by H. B. Willman and J. Norman Payne) 
 
"7T" 
 
 DRIFTLE55 
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 MARGIN OF 
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 SCALE 
 
 5 10 15 20 M I . 
 
 SPRINGFIELD® 
 
 ^ r— I 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 GLACIAL GEOLOGY IN NORTHEASTERN ILLINOIS 
 
 Compiled by George E. Ekblaw from data furnished by the Survey 
 
 January 1, 1942 
 
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