Xfc-3 /*Y 1- 4 5 li &s- - W* Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/cave.inrockareaha1948raas STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION STATE GEOLOGICAL SURVEY DIVISION Morris M* Leighton, Chief CAVE IN ROCK A REA Hardin County- Guide Leaflet iJS-A by Gilbert 0. Raasch Urbana, Illinois 1. '- >l ):l "I . '. ^ /: -:. • c. "'"'•'" tfi : .'' , :.'\ I ■ : . it . ' - • .--.'■: r i ■ . -. . : < , ; , : j. . ■ : 'TO'.' ■'■.'• ■ : - 3 - north (see cross-section of eastern Hardin County.) Going southward the road ascends the north slopes of the hills by long, gentle grades corres- ponding roughly to the dip-slope of the formations. The south hill slopes, on the other hand, are short and steep, where hard layers have been cut through by erosion. These steep slopes resulting from the beveling of the exposed edges of formations are called "escarpments." 30.4 Cross Karbors Ridge Road. 30.7-9 Roadcuts in Caseyville (Pennsylvanian) Sandstone. 32,0 Roadcut showing beds of Tradewater Groups (Pennsylvanian); sandstone over- lying shale. 35.2 Rosdcut Hardinsburg Sandstone on Golconda Shale; both Upper Mississippian. Road makes steep descent down escarpment. 37.3 Roadcut in Rosiclare Sandstone (Lower Mississippian) forming escarpment, 37.6 Junction with State Highway No. 146, Turn right (W) on No. 146. 39.3 Turn right (NJ on gravel road. 39.4 STOP No. 6. The Lower Chester (Lower part of Upper Mississippian) escarp- ment rises about a mile north and is dotted with fluorspar mines. This same escarpment extends nearly 200 miles southeast through Kentucky, where it is called the Dripping Springs Escarpment. In the St. Genevieve and St. Louis Limestones below and at the foot of the escarpment, great caverns have developed, among them Mammoth Cave. Here between us and the escarpment, the rolling, pitted sink-hole topography can be seen. The large lake to the northeast may be present for years only to disappear suddenly, as its water escapes underground. When this underground drain becomes plugged with sediment and debris, the lake again comes into being. 40.8 STOP No. 7. Mi ne of the Crystal Fluorspar Co. Pope and Hardin Counties in Illinois and the adjoining part of Kentucky produce the bulk of U. S. fluorspar. Fluorspar is used principally as a flux in steel manufactur- ing, but fluorine enters into the manufacture of high-octane gasoline, refrigerants, plastics, insecticides. Fluorspar and compounds made from it are used in manufacturing glass, enamel, and aluminum. Illinois fluorspar occurs either in veins along or close to fault zones, or in flat-lying blanket deposits. The latter near the top of the St, Genevieve Formation in a zone between the Rosiclare shale and sandstone above, and the Fredonia limestone below. The present mine exploits such a blanket deposit. Calcite as well as small quantities of galena (lead ore) and sphalerite (zinc ore) occur with the fluorite. The fluorspar deposits are believed to have been formed when the region was undergoing the extensive fracturing, faulting, and folding for which it is famous. Warm solutions from deep in the earth and carrying mineral matter in solution deposited the minerals in crevices, as veins, or as a replacement of the Fredonia limestone in the blanket deposits. If: .;.. ) ■' ., . ! i..v. •; ,q.i -..,.,. ■ • ' ■ | ' 4- . J : ■ ' ' ' - 4 - Elsewhere in Hardin County, molten lava-like rock oozed up in fractures and deposited "dikes" of greenish-black peridotite. This is the only ' igneous rock which comes to the surface in Illinois. 40.8 Reverse route to highway. 42.3 Junction with State Highway No. 146; turn left (E) on No, 146. 44.0 Junction with State Highway No. 1; turn right (S) on No. 1. 45.9 Turn right (E) in Cave in Rock, onto road to State Park. 46.4 STOP No. 8. Cave in Rock parking area. Take trail to the cave. This caveis a modest example of how underground water, moving along joint crevices, dissolves away some limestones to produce caverns. No cave deposits formed in this cave, probably because of its open proximity to the surface. The cave is developed in the St. Louis (Lower Mississippian) Limestone. rr J - 5 - GEOLOGIC HISTORY OF HARDIN COUNTY DEEPLY BURIED FORMATIONS The oldest bedrock which comes to the surface in Hardin County is Devonian in age and outcrops in the center of Hick's Dome, in the western part of the county. A deep oil test well, drilled on the dome in 1935 and deepened in 1944, penetrated to a depth of 3300 feet below the surface and passed through Devonian, Silurian, and Ordovician strata. There is no reason to doubt that, had it gone deeper, the boring would have encountered Cambrian strata below the Ordovician and eventually a Pre-Cambrian "base- ment complex" of igneous and metamorphic rocks. EXPOSED FORMATIONS All of the bedrock strata of the county originated as sediments in the later part of the Paleozoic Era. In the major portion of the area, rocks of Mississippian age outcrop or immediately underlie the loose surface ma- terial. The occurrence of older Devonian strata in the central portion of Hick's Dome has already been mentioned; the beds are limestone overlain by black carbonaoeous shale. Along the northern and eastern edges of the county, and also in some down-faulted "graben" areas, younger beds of Pennsylvanian (Coal Period) age are present above the Mississippian strata. MISSISSIPPIAN SYSTEM For convenience, in terms of the local-area, the Mississippian formations of Hardin County are separated into two divisions, the "Lower Mississippian," involving the Kinderhook, Osage, and Meramec groups, and the "Upper Miss- issippian," coinciding with the Chester Group. Of the "Lower Mississippian," we see only the two upper formations, the St. Louis and the St. Genevieve. These are both thick limestone formations which extend over many thousands of square miles in the Mississippi and Ohio Valleys. The overlying Chester Group, or "Upper Mississippian," is far more complex, and consists of an alternation of relatively thin formations of limestone, sandstone, and shale. In the "Lower Mississippian" formations of Hardin County, all fossils found have been of marine origin, including large numbers of the coral Lithostrotion canadense in the St. Louis Limestone. In the Upper or Chester Division marine fossils of great variety occur in the limestone formations whereas remains of land plants occur rarely in the sandstone formations. A thin coal seam is present in one of the Chester sandstones (Tar Springs Formation.) The Upper Mississippian formations total more than 1000 feet in thickness in Hardin County. ' .i . : 6 - PENNSYLVANIAN SYSTEM A great thickness of Pennsylvania!! strata once overlay the present surface of H ardin County, but erosion has since stripped it all away, except in limited areas, as mentioned above, where a part of this thick succes- sion still remains. The most prominent Pennsylvanian group in Hardin Coun- ty is the basal one, the Caseyville, consisting mainly of thick masses of sandstone, in places studded with white quartz pebbles. Less conspicuous in outcrop are beds of shale, and locally there is a 26-inch coal bed (Battery Rock Coal.) The Caseyville Group reaches a thickness of 400 feet in Hardin County. Fossil ferns are sometimes found in some of the shale beds. Above the Caseyville Group, in Hardin County, are limited areas under- lain by strata of the Tradewater Group. These beds are not notably dis- similar to the Caseyville, except that there is a higher proportion of shale and quartz pebbles do not occur. The 300 feet of Tradewater beds present in the county include two thin coals and a six-inch limestone layer that contains marine fossils. EARLY GEOLOGIC HISTORY Between Pre-Cambrian Time, when the basement complex was formed and then worn down to a nearly level plain ("peneplain"), and the beginning of Upper Mississippian deposition, the area of H ardin county was much of the time, covered by the salt waters of shallow seas that invaded large areas of the North American Continent. At intervals when the seas withdrew the region was generally a low coastal plain. No prominent amount of folding or fracturing took place during these hundreds of millions of years of geologic time, With the beginning of Upper Mississippian (Chester) Time, the crust evidently became somewhat less stable, with alternate rising and sinking of the area to a moderate degree. This let in sea waters for relatively short periods. At other stages, fresh waters formed coastal lakes and lagoons. Under these conditions, sand and clays wore deposited, which con- tained remains of land plants and which hardened to the present sandstones and shales* In Pennsylvanian Time, in southern Illinois, the conditions just de- scribed became progressively more extreme, so that there are repeated successions of land, fresh water, and marine stages, with the marine element becoming much more limited than in the upper Mississippian. Along the Atlantic Coast and to the South in Arkansas, Texas, and Oklahoma, mountains were beginning to rise. As erosion attacked these rising areas, great quantities of pebbles, sand and mud were washed into the Illinois basin. During stages when vast coastal swamps prevailed in the Pennsylvanian days the rich coal fields of Illinois originated as thick masses of half de- * cayed vegetation accumulated in the swamps. - 7 - DISTURBANCE OF EARTH'S CRUST The strata of southeastern Illinois have suffered more disturbance than probably any other area in the Mi ss i ss i ppi Valley. (This, of course, excludes disturbances before Cambrian Time.) This crustal disturbance re- sulted in the formation of large, prominent folds and of an intricate system of faults. Within the area of the field trip, the most spectacular feature is the "graben" area extending NE-SW diagonally across the field trip area, A "graben" is a long narrow down-dropped segment of the earth's crust. The graben itself is fractured and broken'by secondary faults (see cross-section.) Probably at the same time molten igneous magma from deep in the crust intruded the strata along crevices and solidified as greenish- black peridotite. More rarely, deep-seated explosions of gas or steam tore through the bedrock, fracturing it violently and blowing up fragments of other rocks from thousands of feet below the surface. One such occur- rence is the Sparks Hill breccia seen on the trip. Hot liquids and gases, rising at the same time as the lavas, carried mineral solutions and de- posited lead, zinc, and fluorspar in veins or in dissolved-out portions of the limestone layers. The time of these disturbances is generally considered to have co- incided with the elevation of the Appalachian Mountains in Permian Time, which followed the Pennsylvanian to close the Paleozoic Era. LATER GEOLOGIC HISTORY After the deposition of the Pennsylvanian strata in Hardin County, there is no evidence that seas ever again extended into this area, although in Cretaceous time the Gulf of Mexico reached as far north as southern Pope County, Evidently since Pennsylvanian Time, the region has existed as land area that has been undergoing erosion. At some stages, the streams wore the surface down to a nearly flat plain; then, when the whole region was uplifted some hundreds of feet, the streams again began to cut the country up into steep, more or less flat-topped, ridges and deep ravines and valleys, much as it appears today. This succession of stages of rugged and of nearly flat topography took place at least four times, according to R. D. Salisbury. At a level of about 600 feet above the sea lies the most extensive area of flat-topped hills in the region, which clearly repre- sents an old plain of erosion (peneplain) that has since been cut up by leg^jpr erosion. ICE AGE HISTORY Hardin County lies south of the limit of Pleistocene glaciation, but its surface suffered indirect changes due to the glacial conditions. Previous to the Ice Age, the Ohio River did not exist, but in its place were a number of short streams, most of which drained northward. Then the continental ice sheet advanced and halted just north of where the Ohio flows today. The prodigious amount of water resulting from the melting ••■'■> » :s , I «. ' ? <-. i i - ; ! V"! '. • f ■ f : ■. * i ,'■. } „ " ' i ; ; . >; - : ' •• •i ■ „ , .; ,';;! K.'ir. f ;'£' . '•'.: i ' ■ f . . t .Bi •! ■ — ' » ;..; tf d ;.r • '1 '.■i ..ii'i: . z ; • !;■■:■ f~.' •'- ■ ''-'■■ I; . ■!>:.•«' -rf. . t; .. ' v* .' .;.! , • •"' '?,? ;?;•' 7.*j ; !i •j ', ..■ ••; ■ O ;", /:•■,-': ■ '• ■: : ;:.•';' i • ' t ■ ■• ■ \ ■ :.Ci ■: .: j • ; \ • i " i . T-"l' '»'■■"• !■■ . . ■ - ■ : : « ■ r •;;' ■■■;: ; ..- •, *»• '- V"! m 8 - ice could not escape northward as previously because the streams there were blocked by the ice sheet. First they developed lakes in their headwaters, then the water spilled over from one damme d-up valley to the next, and eventually the escaping waters cut their way through the divides, and the Ohio River came into being. v : r. ( i;^w ; i :■ t; en H o a. m 2 S < 01 m CD > U r w