557 ( IL6gui 1961-B State of Illinois Department of Registration and Education STATE GEOLOGICAL SURVEY DIVISION John C. Frye, Chief GEOLOGICAL SCIENCE FIELD TRIP CUIEE LEAF NAMIITON akea HANCOCK COUNTY KEOKUK, CARTHAGE, FORT MADISON, AND LOMAX QUADRANGLES Leaders I. Edgar Odotn, George M. Wilson, G. M. Dow, Paul Dohm, Ed Cording Urbana, Illinois May 6, 1961 GUIDE LEAFLET 196 IB HOST: HAMILTON COMMUNITY HIGH SCHOOL To the Participants: It has been said that the landscape is truly beautiful only when we intelligently understand the varied forces that have worked through the ages to develop it. The result of this understanding is increasing enjoyment and appreciation of the natural features about us. The Geological Science Field Trip program is sponsored by the Illinois State Geological Survey. It is designed to acquaint you with the Illinois landscape, the rock and mineral resources, and the geolo- gical processes that have led to their origin. With this program, we hope to stimulate a general interest in the geology of Illinois and a greater appreciation of the state's vast mineral resources and their importance to the over-all economy. We encourage you to ask the tour leaders any questions that may occur to you during the trip. Discussion often clarifies points that otherwise would remain confused to many of the participants. We also invite your written comments upon the trips, so that we might improve them as much as possible. Additional copies of this guide leaflet, as well as itineraries for trips that have been held in the past, may be obtained free of charge by writing to the Illinois State Geological Survey. Maps are available for 30 cents each. We hope you enjoy today's trip and will come again. ***** Abstract Pleistocene deposits and Pennsylvanian and Missis- sippian rocks are exposed in the field trip area. The Pleisto- cene deposits include Kansan and Illinoian tills, interglacial deposits, and Wisconsinan loess. Pennsylvanian sandstones, shales, and coal seams crop out in isolated patches on the higher hills. These scattered remnants are all that remain of what once must have been a thick sequence of Pennsylvanian rocks. Middle Mississippian, or Valmeyerian, rocks are well exposed throughout the field trip area. The St. LouIb, Salem, Warsaw, Keokuk, and Burlington formations are all represented. The type section for the Warsaw is near the town of that name located just south of Hamilton. The Keokuk type section is just across the river in Iowa and that of the Burlington is only a few miles north at Burlington, Iowa. Lithologic vari- ations in this sequence of limestones, shales, and sandstones are discussed. The occurrence of geodes in the Warsaw is em- phasized and a mechanism of brecciation of the St. Louis Lime- stone is suggested. Other geological phenomena considered on the trip are the origin and significance of sand dunes and loess de- posits and the geologic history of the Mississippi River. Suggested References for Further Study of the Geology of the Field Trip Area 1. Guide Book, Fifteenth Annual Field Conference, the Kansas Geological Society, Central and Northeastern Missouri and adjoining area in Illinois, 19^1* 2. Illinois State Geological Survey, Bulletin h^k, Geology of the LaHarpe-Good Hope Quadrangles , 1921. 3. United States Geological Survey, Folio 208, Geology of the Macomb -Colchester Quadrangles . k. Van Tuyl, F. M., "The Geodes of the Keokuk Beds," Am. Journ. Sci., series h, fol. J+2, 1916, pp. 3^ -te. Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/geologicalscienc1961illi HAMILTON GEOLOGICAL SCIENCE FIELD TRIP ITINERARY Suggestion: Have someone read the guide as we travel through the countryside so that the driver will be able to learn the geology of the area, also. 0.0 0.0 Caravan assembles at Hamilton High School in parking lot behind the school. 0.0 0.0 Turn left (east) on Laurel Street. 0.2 0.2 STOP. Turn right on Highway 96 (south). 0.6 0.8 CAUTION. Railroad crossing. 0.0 0.8 Note outcrop of Keokuk and Warsaw formations on right and left along Railroad Creek. 0.5 1.3 Turn right (west) on gravel road. 0.3 1.6 Turn right. 0.5 2.1 STOP 1. Gray's Quarry. (DO NOT GO NEAR THE EDGE OF THE QUARRY FACE) In the quarry face the geode bearing Warsaw Shale and the Keokuk Limestone are exposed. The Keokuk and underlying Burlington Limestones are quarried extensively in the area. As commonly recognized in this region, the Warsaw formation consists of two parts, the geode bearing beds below and an upper shale character- ized by few geodes. Only the lower portion of the Warsaw formation is present in this section. It contains geodes in great abundance, but very few fossils. The Keokuk Limestone is characterized by massive, evenly bedded cherty limestone with thin shale beds separating some of the limestone layers. In some areas the limestone becomes very cherty at the base. This cherty zone, about 40 feet thick, has been called the Montrose Chert member. The geodes that occur in this area are .prized by mineral collectors all over the world. This will be one of the best opportunities for collecting. If you wish to return to this spot at a later time, please obtain permission. s -2- The Gray's Quarry section is as follows: - •■&>- _..J_J- I ep ir— (- era UJlii 3=mn=rzc Shale, green, many geodes Limestone, blue-gray massive, some shale partings Limestone, with chert stringers and some shale near base Limestone, cherty Dolomite, buffish gray, some imperfect geodes. Limestone, numerous thin shale partings and discontinuous stringers of chert. Limestone, blue gray, cherty ,d" ±--«.vt- .L-JL -^ -_L j- Quarry Floor Scale 1 # = 10 1 0.2 2.3 City of Keokuk, Iowa, across river. 0.1 2.4. View of Keokuk Dam. 0.1 2.5 City limits of" Hamilton. 0.0 2.5 Outcrop of Keokuk Limestone on right. 0.1 2.6 CAUTION. Railroad crossing. 0.1 2.7 Bridge over Railroad Creek. 0.1 2.8 STOP. Continue ahead. 0.1 2.9 STOP. Continue ahead on Highway 136. 0.1 3,0 Abandoned quarry on right — Keokuk Limestone. 0.2 3.2 CAUTION. Turn left on Highway 96. ORIGIN OF GEODES Geodes are usually globular although they also may be irregular, discoid, or sometimes shaped very much like fossils. They are usually found in limestone, but they may also form in shaly rocks. Most of them are hollow, but many have become filled with minerals growing from the walls inward. A typical geode sawed or broken in two will disclose a sequence of layers from the outside-in as follows: 1. A thin clay layer. 2. A layer of noncrystalline chalcedony. 3. Crystals (usually quartz) pro- jecting into the hollow interior. (Less commonly calcite or dolomite crystals will form next to the outer chalcedony layer instead of quartz, and sometimes the inside of a geode will be nothing but chalcedony.) 4. A deposit of minor minerals, commonly as drusy crystals such as pyrite, ankerite, magnetite, hematite, kaolin, aragonite, millerite, chalcopyrite, sphalerite, limonite, smithsonite, malachite, gypsum, fluorite, barite, marcasite, goethite, pyrolusite, and possibly tenor - ite and chalcocite. Perhaps the most thought provoking and rarest of geodes are those which contain petroleum or some thicker bituminous material. By what processes and under what conditions did these interesting features originate? There are many theories, none of which are com- pletely adequate. The following discussion is an attempt to compile some of them into a brief summary. First of all, it is generally agreed that geodes are cavity fillings. The agreement ends here, for the stumbling block is the origin of the initial cavity. One idea is that the cavities are "vugs" caused by gas pockets or shrinkage of the rock. However, vugs are integral parts of the rock in which they are contained, whereas geodes are complete entities which can be broken out of the rock formation with comparative ease. Some have suggested that they are merely special types of concretions; but geodes grow from the outer shell inward, whereas concretions build up from a central core. Bassler (Bassler, R. S. , The Formation of Geodes , with Remarks on the Silicification of Fossils, National Museum Proc. , Vol. 35, 1908, pp. 133-154) has shown that some geodes originate in fossil cavities and upon growth of the geode, the fossil bursts. Upon further growth, the fragments of the fossil are dissolved or absorbed by the growing geode and are lost. Van Tuyl (Am. Jour. Sci. , Series 4, Vol. 42, 1916, 34-42) believes that the original cavity is the space which was occupied by a concre- tion. Concretions are easily removed from the rock by percolating waters and would thus leave a likely spot for a geode to grow. The fact that some geodes contain calcareous clay concretions lends support to this theory. Petti John ( Sedimentary Rocks , Harper and Brothers, New York) gives a rather complex process by which geodes grow after the formation of an initial cavity which may be summarized in the following steps: 1. A cavity is formed in the rock by some means. 2. A salty solution fills the cavity and pore spaces in the rock. 3. A layer of gelatinous silica is then deposited isolating the salt solution in the cavity. k Later the water in the surrounding pore spaces becomes fresh. This sets up what is known as an osmotic cell. This particular osmotic cell consists of two different types of solutions separated by a membrane of gelatinous silica which will allow the fresh solution to pass into the geode cavity, but will not allow the salt to pass out of it. 5- The fresh water flowing into the cavity by osmosis builds up internal pressure which pushes on the walls of the geode. 6. This pressure, exerted outward against the surrounding limestone, dissolves the lime- stone leaving an insoluble residue which becomes the thin clay layer on the outer surface of the geode. 7- The above process continues until the salt solution is so diluted by the incoming fresh water that the osmotic cell no longer operates. The geode has reached maturity. 8. Gradually the silica gel dehydrates and crystallizes. 9- Shrink- ing and cracking then follow. 10. Finally mineral bearing waters flowing through the cracks deposit the innermost layer of minerals. These cracks may eventually seal leaving a completely closed geode. The process by which some of the geodes of the Warsaw beds came to contain petroleum is very much a mystery, also. In an article appearing in Earth Science, Vol. ih, No. 1, Feb., 1961, Frank Fleener gives an interesting account of the problem. He envisions the petro- leum migrating up to the Warsaw Formation from oil bearing rocks to the south. Here partially formed geodes were encountered and loose quartz crystals (some doubly terminated) were set adrift in the thick bitumen. The influx of the bituminous material stopped the growth of the geodes, but the mechanism by which the bitumen was enclosed and hermetically sealed remains a matter of conjecture. We believe that many of these geodes are hermetically sealed because the bituminous material will sometimes squirt out with force when the geode is punctured. This phenomenon is presumably due to the sudden expansion of the material when the pressure under which it was formed is relieved. A more plausible explanation for the petroleum is that it was derived from the enclosing shale and shaly limestone. The weight of overlying materials could easily free hydrocarbons from the organic matter in the shale and shaly limestone which then migrated to the area of least pressure. The low pressure area would likely be in the cavity inside the geodes. It appears that such a pressure difference would exist because the hard shell of the geode could withstand a great amount of lithostatic pressure. This discussion is incomplete and generalized, but we hope that it will stimulate interest in these remarkable features. Perhaps as you break them open in search of beautiful crystals, you will reflect upon their history and come to a greater appreciation for the intricate processes by which nature is continuously altering the crust of the earth. -3- 0.1 3.3 STOP. Continue ahead on Highway 96. Note sand dune on right and abandoned quarry on left. 0.4 3.7 Bridge over Chaney Creek. 0.1 3.8 Outcrop of Keokuk Limestone on left. 0.9 4.7 Bridge. 0.1 4.8 Outcrop of Keokuk Limestone on right. 1.1 5.9 Bridge over creek. 0.2 6.1 Note rounded slopes of bluffs capped by loess and fine sand. Sand dunes are abundant in the area as we will see at Stop 4. 0.5 6.6 Abandoned quarry in Keokuk Limestone on right. 0.1 6.7 Outcrop of lower Warsaw Shale and Limestone on right. 0.8 7.5 Bridge over Wagoner Creek. 1.1 8.6 Bridge over Larry Creek. 0.1 8.7 Abandoned quarry in Keokuk and Warsaw Formations. (See Larry Creek Section) 0.3 9.0 This hill is called Mt. Mariah. 0.1 9.1 Salem Sandstone and St. Louis breccia on right. The Mount Mariah section is as follows: Pennsylvanian sandstone St. Louis Formation: Breccia composed of gray Is. and dol. cobbles, slabs, blocks, angular shaped, in distorted dolomitic shale matrix. Salem Formation: Dolomitic sandstone, cross-bedded, with glauconite near top The Larry Creek Section is as follows: Upper Warsaw Upper Shale, buff to gray, calcareous, weathers to a steep slope Lot a. t r „?J E5 - 4 - KeokoK '(" Shale, gray, calcareous Limestone, gray, finely crystalline, cherty Limestone, gray, finely crystalline, single bed, shaly parting Limestone, gray to drab, fine grained with chert and calcite filled vugs - 2" gray shale at base Limestone, dark gray, crystalline Shale, gray, very calcareous Limestone, gray, finely crystalline, much chert 25' Lower Warsaw Limestone, buff, very earthy, with geodes 12' Shale, gray, calcareous 3' Limestone, gray, fine grained, argillaceous 3' Limestone, buff, very earthy with geodes 5* Upper Keokuk Limestone, gray finely crystalline, with 3' shale at base, gray, calcareous, with many bryozoans Limestone, gray, finely crystalline, chert 3% at base 2' 4' 3' V -4- 0.4 9.5 Keokuk Limestone on right. 0.3 9.8 Small brook. 0.3 10.1 Outcrop of Keokuk Limestone on right. 0.3 10.4 Outcrop of Keokuk Limestone on right. 0.1 10.5 This portion of Illinois 96 will be part of the Great River Road. It will extend from Cairo to the northern border of Illinois, following very closely the Mississippi River. A portion of this road is now under construction between Hamilton and Warsaw. 1.1 11.6 Note high loess-covered bluffs on Iowa side of the Mississippi. 0.2 11.8 STOP 2. Abandoned quarry in Warsaw Shale and Keokuk Limestone. In this abandoned quarry the lower geode bearing Warsaw Shale and the upper beds of the Keokuk Limestone are exposed and accessible for examination. The Warsaw contains numerous geodes. The best place to collect them is in the stream just to the south of the quarry. Fossils are abundant in certain beds of the Keokuk Limestone. Brachiopods and crinoids are the most abundant. Note the shale partings between the limestone beds and the white chert inter-bedded in the limestone. Both are impurities and make the stone less valuable than if they were not present. 0.2 12.0 CAUTION. Turn right on gravel road. 0,1 12.1 Outcrop of Keokuk Limestone on left overlain by brownish yellow loess. 0.3 12.4 Peorian loess on left. 0.3 12.7 Vineyard on left. This soil is very well adapted for the growing of grapes. A rather large wine industry flourishes in the region. 0.5 13.2 Excellent soil profile in cut bank on right. 0.3 13.5 Note slumping of loess on the right. 0.1 13.6 Turn left (north). 0.8 14.4 T-road east. Continue ahead. 0.2 14.6 Note excellent outcrop of loess on right. 0.1 14.7 STOP 3. Outcrop of brecciated St. Louis Limestone. Along this creek, the brecciated St. Louis Limestone is exposed. The rock is a jumbled mass of irregularly disposed sub-angular blocks of compact gray limestone. How such a breccia could form has been a -5- subject of much controversy. Perhaps one of the better explanations is that layers and veins of gypsum and anhydrite which were inter- bedded with the limestone were dissolved out, thus leaving room for the limestone to settle and break under the force of its own weight (and perhaps also under additional weight of overlying strata which may or may not have existed at the time) . This theory is supported by the fact that such gypsum beds have been found farther south in stratigraphically equivalent rocks which are more deeply buried. At another stop, we shall see more of this brecciated limestone along with other rocks which underlie it. 0.1 14.8 SLOW. Bridge. 5-ton limit. 0.1 14.9 Turn left (west). 0.5 15.4 Note the flatness of the upland surface. 0.2 15.6 House on left is constructed of native sandstone which comes from the base of the Salem Formation. 0.4 16.0 T-road. Turn right (north). 0.5 16.5 Turn left (west). 0.1 16.6 The abandoned church on left is constructed of native sandstone. 0.3 16.9 Outcrop of geode-bearing Warsaw Limestone and Shale in creek on right and left. 0.1 17.0 CAUTION. Bridge over creek. 0.1 17.1 Abandoned cheese or wine cellar on left in side of hill. 0.4 17.5 Orchard on right. The soil is also very good for growing fruit. 0.1 17.6 Large vineyard on left. 0.1 17.7 Building on right was constructed in 1846, during the Mormon era in Nauvoo . 0.2 17.9 Gem City Wine Company on left. Most of the grapes grown in this region are used for making wine. 0.5 18.4 Entering Nauvoo State Park. 0.4 18.8 Turn right. 0.1 18.9 Turn left. STOP 4. Lunch. Pavilion in Nauvoo State Park. Outcrop in park shows 15 feet of fine sand overlain by about 8 feet of loess. Sand dunes are quite plentiful in the field trip area and this exposure illustrates some of the features characteristic of dunes. Sand dunes assume many shapes according to the way in which they are formed . -6- Often the shape of the dune vill indicate the prevailing wind direction at the time of its formation. We cannot tell much about the external shape of the dune that is exposed in this area, however, because it is obscured by the loess which overlies it. We can, however, see cross -bedding, one of the most characteristic internal features of dunes. Cross -bedding results from variations in wind direction and slope angle of the dune itself. These dunes and the loess formed during the last, or Wisconsinan, glacial stage as melt water poured down the Mississippi River Valley. In summers, the valley of the Mississippi was flooded by water from the melting glacier. In the winters, when little melting occurred and the floods subsided, the sand and silt in the valley were exposed and dried and strong winds spread the fine material over adjacent uplands. The severe climate which prevailed at the time also inhibited vegetation, thus exposing the land to wind action. If we examined in detail the size of the silt composing the loess along a straight line from the Missis- sippi River eastward, we would find that the particles become smaller and smaller. The deposits also become thinner in an eastward direction, gradually dying out. It is evident that the wind deposited the larger particles first, carrying the lighter particles farther from their source The Pleistocene Epoch Since we have been talking about material that was deposited during the "Ice Age," or Pleistocene, a little background information seems in order. This will help you to better understand the rather complicated relationships to be encountered at future stops . Tens and hundreds of thousands of years ago most of Illinois, together with most of northern North America, was covered by huge ice sheets or glaciers . These glaciers expanded from centers in what is now eastern Canada. They developed when the mean annual tempera- tures in the region were somewhat lower than now, so that not all of the snow that fell during the winters melted during the summers. The snow residues accumulated year after year until a sheet of ice was formed so thick that, as a result of its weight, the lowermost part of it began to flow outward, carrying with it the soil and rocks on which it rested and over which it moved. The process continued until the gla- cier extended into our country as far south as Missouri and Ohio Rivers. When the glaciers melted, all of the soil and rocks which they had picked up as they advanced were released. Some of this material, or drift, was deposited in place as the ice melted. Such material consists of a thorough mixture of all kinds and sizes of rocks and is known as till . Some of the glacial drift was washed out with the meltwaters. The coarsest outwa sh material was deposited nearest the ice front and gradually finer material farther away. The finest clay may have been carried all the way to the ocean. Where the outwash material was spread widely in front of the glacier, it forms an outwash plain ; where it was restricted to the river valleys, it forms valley trains. -7- At times, especially in the winters, the outwash plains and valley trains were exposed as the meltwaters subsided, and the wind picked up silt and fine sand from these surfaces, blew it across the country and dropped it to form deposits of what is known as loess . Glacial loess mantles most of Illinois. Near the large river valleys, it may be as much as 60 to 80 feet thick. Far from the valleys, it may be measured only in inches if it can be identified at all. In the Pleistocene Period (or "Great Ice Age"), North America experienced four successive glacial invasions, each separated by long intervals of mild climate. Of these four invasions, the earliest, the Nebraskan, may have extended into this region. The second, or Kansan invasion, moving down from the region east of Hudson Bay, extended over the Hamilton area. When the Kansan ice sheet melted away, it left behind glacial drift, rock and debris which mantled the surface and concealed the bed- rock. There followed a long interglacial interval (the Yarmouthian Stage) , which left its record in the form of old soils and weathered zones on and in the Kansan glacial drift. From the amount of weathering and leaching that affected the Kansan drift, the length of the Yar- mouthian Interglacial Stage is estimated at from 200,000 to 300,000 years. The Yarmouthian Interglacial Stage was terminated by the advance of a -?ew glacier, from a center of accumulation east of Hudson Bay. This Illinoian Ice Sheet is well named, for not only did it cover nearly all of Illinois, but its western termination coincides closely with the western boundary of the state. Illinoian deposits are well exposed in the Hamilton area. After several thousands of years, climatic conditions caused the melting away of the Illinoian Ice Sheet. During this warm stage, the upper part of the Illinoian till was weathered and soil developed, just as in the case of the preceding Yarmouthian interval. However, this action did not take place to the degree it did during the Yar- mouthian, so that the post-Illinoian (Sangamonian) interval is estimated to have lasted only about 150,000 years. The Sangamonian interval was brought to a close by the fourth and final readvancs of the glaciers. This Wisconsinan Ice Sheet never reached the Hamilton area. It left its mark on the region, nevertheless . The Mississippi and other streams were choked with sedi- ment washed out from the ice fronts that stood to the north and east. The frigid blasts that whipped across these broad sand and mud flats caused violent dust storms. The dust accumulated on the uplands and covered the Illinoian drift and Sangamonian soils with a thick layer of loess. This ashy loess, over most of the upland, grades into the soil of the present day. 0.0 18.9 Turn left (west). 0.1 19.0 CAUTION. Turn right on Highway 96 (north). STAGES OF GLACIATION Nebraskan (1st Stage) Kansan (2nd Stage) V Illinoian (3rd Stage) Wisconsinan (4th Stage) -8- 0.1 19.1 City limits of Nauvoo. 0.2 19.3 Turn right on Highway 96. Entering Nauvoo business district. 1.1 20.4 Turn left, S curve. 0.2 20.6 Historical marker. Marker reads as follows: "Historic Nauvoo. In 1839 the Mormons or Latter Day Saints settled at Nauvoo and made it their chief city. During their residence its population reached 15,000. After long friction with non-Mormons the Mormons were expelled in 1846. Three years later, French communists called Icarians estab- lished a society here which lasted until 1857." 1.9 22.5 Outcrop of loess on left. 1.0 23.5 Turn left (north). Continue ahead on Highway 96. 0.6 24.1 Nauvoo High School on right. 0.3 24.4 Note extreme flatness of the upland surface. This flatness is an indication that the Mississippi is a relatively new stream. It has not had the opportunity or time to extend tributary valleys into the uplands. This flat area is capped by loess overlying Illinoian and Kansan tills. 2.3 26.7 STOP 5. Outcrop of Petroliferous Geode-Bearing Warsaw Shale and Limestone These Warsaw Shale and Limestone beds contain petroliferous geodes, occurring in the bottom of the bed. The Warsaw in this section consists of bluish, argillaceous shale with thin layers of dolomitic limestone. Some of the limestone is fossiliferous, but collecting at this location is rather poor. A word of caution - the bituminous material in these geodes is detrimental to clothing; once on the fabric, it tends to stay in spite of all effort to remove it. 0.2 26.9 Warsaw Shale and Limestone exposed along Tyson Creek on right and left. 0.6 27.5 SLOW. Turn right. Warsaw Shale and Limestone outcrops in small creek on right and left. 0.7 28.2 Turn sharp right, then left. 0.5 28.7 Turn right. Jackson Cemetery on left. 0.1 28.8 Turn left. 0.1 28.9 STOP. Turn left on blacktop road. -9- 0.1 29.0 STOP 6. .Jackson Cemetery Section The profile is as follows: Peoria Loess Gray brown, leached of carbonates 7' Farmdale Loess Gray with pinkish cast, leached 1' Sangamon Soil A Zone Dark gray and leached 2* B Zone Brown, liminitic and leached l 1 C Zone Till, gray, iron stained oxidized and leached 3' The soil that developed upon the Illinoian till is now a fossil (paleosol) or buried soil. Covering this soil are two distinct ages of wind-blown silt called loess. Soil is a product of weathering. Like many other things, rocks and minerals suffer changes when they are exposed to the weather. Al- though these changes &r.'i relatively slow, they become evident in earth deposits thai are act disturbed over long periods of time and develop what is known, as a weatuering or soil profile. Following the practr.ee established about 35 years ago by the Russian, Glinka, soil scientists usually consider that the soil or weathering profile consists of 3 zones, designated A, B, and C from top downward. The A zone is the "soil" zone, which is normally black or gray in color. The B zone is the "subsoil" zone, and the C zone is the unaltered parent material. The zonal effect results from the fact that the four principal processes which eLfect soil weathering all progress with the downward movement of ground water but at different rates. These processes, listed in order according to their rate of progress beginning with the most rapid, are (1) oxidation, (2) leaching of carbonates (3) decom- position of more resistant minerals, and (4) accumulation of humus. Ideally, then, in the A zone in which humus material derived from decayed plants has accumulated, the rock materials are oxidized, leached, and decomposed. In the upper part of the B zone, they are oxidized and leached and in the lower part of the B zone they are only oxidized. The oxidation zone is recognized by its reddish brown or yellowish color resulting from the oxidation of iron minerals. The leached zone is determined by the absence of carbonates, as revealed by tests with dilute of hydrochloric acid. The paleosol, or fossil soil, exposed in this roadcut is fairly well preserved. It developed upon Illinoian till during the Sangamonian -10- irtterglacial stage. The characteristic properties of the A, B, and C zones depart slightly from the ideal because of the age of the soils. Unlike more recent soils, the parent material is thoroughly altered to such an extent that even the resistant silicates are decomposed. The material resulting from such extreme alteration of tills is called gumbotil by many geologists. Gumbotil is generally a gray, sticky clay that becomes very hard upon drying. In this exposure secondary oxidation of the gumbotil has given it a rusty color. Secondary leaching has removed the carbonates from all zones of the profile. The last, or Wisconsinan, glacier never reached this area, but its effects are re- corded here by the loess deposits that overlie the old Sangamon soil. On the west side of the road, just downhill from the soil profile, is an excellent exposure of Mississippian bedrock. From this exposure, it is possible to learn more about the brecciated St. Louis Limestone that was seen at Stop 3. The section is as follows: St. Louis Formation A breccia, chiefly subangular 15' blocks of compact gray lime- stone. More regular layers of gray 2' limestone. Green shale, irregular at base. Varies in thickness from a few inches to 5 feet. variable Salem Formation Sandstone, very dolomitic, 10' cross-bedded. This exposure shows well the brecciated nature of the St. Louis Limestone. Just below the slumped blocks is a layer of un-brecciated limestone. The presence of this un-brecciated layer lends support to the theory of origin of the breccia which was discussed at Stop 3. If the brecciation had been caused by external forces, either during deposition or later on, one would expect all of the limestone to be brecciated. Since the lower portion is undisturbed, the anhydrite and gypsum beds could have been deposited above it and then dissolved out leaving the beds below unaffected. Below the limestone is a green shale member. This shale may be quite thin in some places and up to 5 feet thick in others. Note the irregular nature of the lower surface. This indicates that a period of erosion took place prior to the deposition of the green shale. Such breaks in the geologic record are called unconformities. Below the green shale the upper portion of a dolomitic sandstone is ex- posed. The sandstone probably belongs to the Salem, although it is not typical of that formation. 1.1 30.1 STOP. Turn left on Highway 96. Entering city of Niota or East Fort Madison. -11- 0.2 30.3 Junction Highway 9 and 96. Continue ahead on 96. 0.1 30.4 STOP. Continue ahead. 0.2 30.6 Leave Highway 96. Go straight ahead on gravel road. 0.5 31.1 SLOW. Bridge over Tyson Creek. 0.1 31.2 SLOW. 0.1 31.3 T-road. Turn right. 0.2 31.5 SLOW. Rough bridge over Tyson Creek. 4-ton limit. Good section of Keokuk Limestone on left. 0.5 32.0 Note outcrop of loess overlain by sand on right. 0.2 32.2 Indian Mound on right. 0.2 32.4 City of Fort Madison directly across the river. 0.2 32.6 Indian Mound on right. STOP 7. Discussion of Mississippi River. The Mississippi-Missouri River system is the longest in the world. The Mississippi drains the great interior of the United States, from the Continental Divide in the West to the Appalachians in the East. Besides the massive volumes of water, the Mississippi carries millions of tons of sediment to the Gulf of Mexico each year. The material which has been eroded from the continent is dumped at the river's mouth where it builds up forming a delta. The delta is being extended each year at such a rate that the port of New Orleans is now an inland city. The river is very wide at this site because the water has been ponded by the Keokuk dam. This dam protects the region from damaging floods for several miles up stream. Old Man River has played a major role in the development of the country. The river and its tributaries form one of the most important inland water ways in the world and was an indispensible supply route of the early settlers. If we are fortunate, we may see a tow boat with barges on the river today. The present volume of river traffic, proves that the Mississippi is still an important route of commerce. The powerful Mississippi has an interesting geological history also. According to present thinking, during the Nebraskan glacial stage, the Aftonian interglacial stage, the Kansan glacial stage, and the Yarmouthian interglacial stage, the Mississippi River turned southeastward north of Cordova and flowed through the Meredosia channel and the Green River Basin to the "big bend" of the Illinois -12- River near Bureau, thence southward to the mouth of the Illinois. The Mississippi Valley above Cordova and the present valley below Muscatine and Andulusia were separate independent drainage systems The advance of the Illinoian (third) glacier over this area into eastern Iowa, blocking the southeastern channel, forced the Mississippi to establish a temporary channel in eastern Iowa. LINN JONES r i i i l -[cedar >. \ ft- JOHNS' o v\i~ WASHINGTON^ AHENRy ILLINOIS COURSE OF THE TEMPORARY MISSISSIPPI RWER During Illinoian Glacial Stage Scale in Miles After Schoewe 1923 -13- This channel in front of the Illinoian ice sheet extended approxi- mately from the mouth of the Maquoketa River, north of Savanna through the Goose Lake channel in eastern Clinton County, across northeastern Scott and Mascatine Counties, westward to southeastern Washington County, and southward through Henry and Lee Counties to the present Mississippi channel near Fort Madison, Iowa, (see figure.) Upon withdrawal of the Illinoian ice sheet, the Mississippi reoccupied its former southeasterly channel to the "big bend n of the Illinois where it remained during the Sangamonian interglacial stage and during the early portion of the Wisconsinan glacial stage. 2.1 34.7 SLOW. Turn right. Descend steep hill into Robinson Creek Valley. 0.1 34.8 Note extreme slumping of loess on the left. 0.7 35.5 STOP 8. Pleistocene Section in Southwest Bank of Robinson Creek. The two tills exposed in this section represent two glacial advances separated by sand, clay, and peaty silt. A few years ago there would have been little hesitation in applying names to the units exposed, but today we will limit ourselves to problems of interpretation of the Pleistocene. Our hesitation stems from recent work by Survey geologists on the Illinoian glacial stage. These workers have discovered convincing evidence that breaks exist in the Illinoian sequence which probably represent retreats and readvances of the glacier. With regard to this section, we do not know at this time whether Kansan till overlain by sand, clay, and peaty silt, in turn overlain by Illinoian till and Wisconsinan loess is represented here or if there is merely two advances of the Illinoian with the deposits separated by the sand and silt sequence. Our knowledge of the earth's history is not complete by any means. We are only beginning to open the door to this vast room, and as we acquire new knowledge, we often must change earlier opinions and inter- pretations. Geology is a dynamic science, and it is difficult to keep abreast of the vast information being accumulated. 0.1 35.6 CAUTION. Bridge over Robinson Creek. 4-ton limit. 0.2 35.8 T-road. Continue ahead. 0.7 36.5 House on left built of native sandstone. 0.3 36.8 Crossroad. Turn right (west). 1.0 37.8 SLOW. Turn left (south). 0.6 38.4 STOP. Turn right. 0.1 38.5 T-road. Continue ahead. 0.1 38.6 Entering City of Nauvoo. Follow Young Street straight through town. 0.9 39.5 Descending into Mississippi River valley. -14- 0.3 39.8 SLOW. Turn right (north). 0.3 40.1 STOP 9. Nauvoo Stone Company Quarry. The section in this quarry is as follows: Keokuk: Limestone, gray to cherty, 10 ' fossiliferous. Burlington: Limestone, gray, fossiliferous. 5* Shale, black, fossiliferous V to 3' Limestone, gray. 2' Shale, black. 6" to 1' Limestone with shale streaks and cherty lenses. 20' to 25' This operation quarries the Burlington limestone for road metal, for mixing with concrete for construction purposes, miscellaneous uses, and some for agricultural lime. The upper limestone or Keokuk is more fossiliferous than the Burlington into which it grades. Consider- ing both limestones together, they are gray to white, crystalline, and crinoidal. Chert bands and lenses as well as vugs of calcite are common. The Keokuk tends to be grayer, more granular and cherty, and more thinly bedded than the underlying Burlington. Among the fossils which may be found at this quarry are crinoids, brachiopods, bryozoa, cup corals, and gastropods. Trilobite fragments, pelecypods, and bones of primitive fish are less common. GENERALIZED GEOLOGIC COLUMN FOR THE HAMILTON AREA ERAS Cenozoic Mesozoic Paleozoic Proterozoxc Archeozoic PERIODS Quar ternary Tertiary Cretaceous Jurassic Triassic Permian Pennsylvanian Mississippian Devonian Silurian Drdovician Cambrian EPOCHS Pleistocene Pliocene Miocene Oligocene Eocene Paleocene Chester Valmeyer Kinderhook FORMATIONS (See detailed Time Table of Pleistocene) . Stream gravels Present in extreme southern Illinois only Not present in Illinois Not present in Illinois Not present in Illinois Sandstones, si It stones, shales, clays, and coal Not present in Hamilton area St. Louis limestone Salem limestone Warsaw limestone and shale Keokuk limestone and shale Burlington limestone - cherty Limestone, some shale at base Limestone and sandstone in deep wells Limestone and dolomite in deep wells Shales, limestone, and sandstones, in deep wells Dolomites in deep wells Referred to as "Pre-Cambrian" time <8r Time Table of Pleistocene Glaciation (after M. M. Leighton and H. B. Willman, 1950, J. C. Frye and H. B. Willman, 1960) Stage Recent Sub st age 5,000 yrs, Valderan 11,000 yrs. Twocreekan ,500 yrs. c CO g o W 1-4 J* Woodfordian 22,000 yrs. Farmdalian 28,000 yrs. Altonian 50,000 to 70,000 yrs." Sangamonian (3rd interglacial) Illinoian (3rd Glacial) 12 Buffalohartan Jacksonvi 1 lian Paysonian (terminal) Love land i an (Pro-Illinoian) Nature of Deposits Soil, youthful profile of weathering lake and river deposits dunes, peat Outwash Peat, alluvium Drift, loess, dunes lake deposits Special features Glaciation in northern Illinois Ice withdrawal, erosion Soil, silt and peat Drift, loess Soil, mature profile of weathering, alluvium, peat Drift Drift Drift Loess (in advance of glaciation) Glaciation, building of many moraines as far south as Shelbyville, ex- tensive valley trains, outwash plains, and lakes Ice withdrawal, weather- ing, and erosion Glaciation in northern Illinois, valley trains along major rivers, Winnebago drift Yarmouthian (2nd interglacial) Soil, mature profile of weathering, alluvium, peat Kansan (2nd glacial) Drift Loess Aficnian (1st interglacial) Soil, mature profile of weathering, alluvium, peat Nebraska- 's;: glacial) Drift TILL PLAINS SECTION, GREAT LAKE SECTION CENTRAL LOWLAND PROVINCE ENTRAL LOWLAND PROVINCE ^INTERIOR LOW PLATEAUS PROVINCE ILLINOIS STATC GEOLOGICAL SURVEY COASTAL PLAIN PROVINCE PHYSIOGRAPHIC DIVISIONS OF ILLINOIS (Reprinted from Illinois State Geological Survey Report of Investigations 129, "Physiographic Divisions of Illinois, " by M. M. Leighton, George E. Ekblaw, and Leland Horberg) (10M— 5-59) ,: » -***«« I? ?fi . > i H ill i GEOLOGIC MAP OF ILLINOIS \<— } f - * s f^l " showing jfe«nlF^ i ^ 1 ,v : T3^ BEDROCK BELOW ^J^I^V^v ^BlfeM^ THE GLACIAL DRIFT 1961 fertiary (Pliocene omitted) Pennsylvanian (Above No. 6 Coal) IB. Pennsylvanian (Below No. 6 Coal) Mississippion (Middle and Lower) LTD Silurian and Devonian ILLINOIS STATE GEOLOGICAL SURVEY, URBAN* 31954-2VaM-3-61 Plate I COMMON TYPES of ILLINOIS FOSSILS Cup coral GRAPTOLITE Lithostrotion CORALS Honeycomb coral CRINOID PENTREMITE Archimedes Fenestella 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 ) Calymene (flat) OSTRACODS (greatly enlarged) TRILOBITES 4&*