s Of 2- & e ^ <£ 9- a m cr to a CO — 5 ■< Q CD r- X O 2* CD 5 P c MINERAL RESOURCE RECORDS DIVISION ILLINOIS STATE GEOLOGICAL SURVEY STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION STATE GEOLOGICAL SURVEY DIVISION Morris M. Leighton, Chief MT. CARROLL AREA Carroll County GUIDE LEAFLET 53 ^ ^ by Arthur C. Be van Urbana, Illinois October 10, 1953 *»"> L«J5 •o -y # «■ Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/mtcarrollareacar1953beva 0.0 0.0 0.0 0.0 0.2 0,2 0.1 0.3 0.2 0.5 0.1 0.6 0.3 0.9 0.0 0.9 0.6 1.5 0.1 1.6 0.1 1.7 0.1 1/8 0.3 2.1 0.1 2.2 Part I. Itinerary Caravan assembles at Shimer College, Mount Carroll. Leave campus and turn right (N) on Clay Street. Jet. with Routes 64-52; turn left (W) . Stop sign. Cross Main Street and descend grade. Road-end; turn right (N) in valley. Park entrance. Turn left into Point Rock Park. Cross bridge and park along roadside. STOP NO. 1. Walk east to Point Rock. This is an outcrop of Galena Dolomite (magnesian limestone) of Ordovician age. Beneath the surface soils of the Mount Carroll region is a consider- able thickness of loose material (gravel, sand, clay, etc.), most of which was dumped here at the time of the melting of the Illinoian glacier. Beneath "this "glacial drift" lies bedrock of great age. The bedrock is exposed chiefly in those places where erosion by streams during or since the Ice Age has cut down through the glacial drift cover. Farther north in the region, Niagara (Hopkinton) dolomite of Silurian Age lies beneath the drift, but tn the south part of the area, older, Ordovician dolomites form the bedrock surface. This is because the strata in the south have been uplifted several hundred feet to form the so-called Savanna anticline (up-fold). The Galena Dolomite is over 200 feet thick. The even stratification of the layers indicates that the rock was deposited in quiet water, and the fossils in the dolomite indicate a marine environment. YJhite chert (SiOg) is characteristic of much of the formation. The Galena Formation takes its name from Galena, Illinois, which in turn is named after the valuable lead sulphide (galena), which occurs in association with zinc minerals in the Galena region. Continue ahead, turn at end of parkway, and return to -- Park exit. Turn right (S) . Turn left (E) and ascend grade to — Main Street; turn left (N). Stop sign. Continue ahead (N) across Franklin Street. Turn right (E) along south side of Court House. Stop sign. Turn left (N) on Clay Street (Route 78) and park caravan. Walk north to bridge over gorge of Carroll Creek. " ■ " r - 2 - STOP NO. 2. Here is seen a much greater thickness of Galena Dolomite, rising close to the top of the gorge wall (about 780 feet A. T.). The Illinoian ice mass and the glacial drift it left behind masked the former drainage pattern of ridges and valleys. Commonly, the streams that reappeared after the glacial retreat found the old, buried valleys. Eut here the post-glacial stream cut down to discover a former rock ridge. This evidently served temporarily as a dam, at a time when the stream was swollen with water from the melting ice that still existed to eastward* As a result gravels washed out from "the ice were deposited along the broad valley up stream. Very likely a water fall existed on the site of the present rock gorge, which eventually developed as the falls retreated up stream. 0,0 2.2 Continue ahead (N) on Route Wo. 78. 2.7 4.9 Descend grade and park adjacent to quarry on right. STOP NO. 3. The quarry exposes nearly 30 feet of Silurian dolomite of Ni agar an (Hopkinton) age. The top of the quarry lies at an elevation of about 730 feet above sea level, which is some 50 feet lower than the Galena outcrop top in Mt. Carroll. To reach this same Galena dolomite at the present stop, it would be necessary to bore down over 250 feet. Such structural differences in a very short horizontal distance are relatively rare in northern Illinois. Evidences of faulting may be found along this same line in the Savanna area, but the fault may have passed into a very steep down-fold ("monocline") farther east. Near the bottom of the quarry and again across the middle are two bands of thick-bedded dolomite jammed with the casts and molds of a large brachiopod, Pen tamer us oblongus . The original shell matter has been dissolved away, and only the impressions in the rock are left behind. Between the upper and lower shell bands, which may be likened to present- day oyster colonies, the Pen t ame ru s is less common and is associated with a smooth, transversely elliptical brachiopod (Stricklandia sp.). The upper 7 feet of rock in the quarry is more granular and porous, lacks the brachiopods mentioned, and contains, rarely, a peculiar, golf ball- like coralloid fossil, C erionites dactyloides . The P entamerus bands, with the Cerionites bed above, extend continuously in this part of the Niagaran throughout northwestern Illinois and north- eastern Iowa. Rocks of similar age in northeastern Wisconsin, upper Michigan, and western New York also have two Pentamerus bands with an interval between. The C erionites has not been found farther to the east, however. 0.0 4.9 Continue ahead (N) on Route 78. 1.3 6.2 Exposiires of Silurian, Edgewood and Kankakee dolomites, of Lower Silurian age are here exposed at elevations below that of the Middle Silurian (Niagaran) beds of Stop No. 3. 0.1 6.3 Cross Plum River. 0.8 7.1 Outcrops of Lower Silurian dolomite on right. - 3 - 0.3 7.4 Cross creek. 0.5 7.9 STOP NO. 4. Park along roadside and walk east into gravel pit. When the Illinois glaciers melted, they dropped the rock, sand, and clay picked up at many points along the 1000 mile course and dropped them as an unsorted blanket of earth and rock called "glacial till". Such un- sorted glacial till may be seen forming the upper 7 feet of the pit. When a glacier melts, it also releases immense quantities of water. When water encounters unsorted material (such as glacial till) a sorting action takes place. The heavy boulders are dropped close to the source, sand and gravel are deposited as bars and banks along the courses of the streams, and the silt and clay are carried off long distances to be deposited in slack waters. The lower 20 feet of deposits in the gravel pit illustrate water-laid glacial deposits, and show stratification and a removal of most of the clay and silt. That the waters were highly turbulent is shown by the presence of large boulders and of fragments of limestone torn from the local ledges. That the deposit was laid down during the glacial period is evidenced by the large numbers of igneous (granite, gabbro, basalt, porphyry) and metamorphic (schist, gneiss, quartz ite) rocks which crop out many hundreds of miles to the north, in the region of Lake Superior and Canada. It is probably that the gravel was laid down just ahead of the advancing ice, where torrential floods of melt water existed in the summer season. That the ice eventually covered the gravel deposit is shown by -the presence of the till above it. However, it did not advance far as we are here within a mile of the west limit of glaciation. At the same level as the gravel, Lower Silurian strata are present just northwest of the pit. This shows that the gravel was deposited in -the head of a small preglacial valley. 0.0 7.9 Continue ahead (N) on Route 78; the route for the rest cf -the morning will be in the "Drif tless Area", which was not covered by glacial ice. 1.6 9.5 STOP NO. 5. Park along ridge top on roadside south of intersection from east. Walk north and descend hill along highway. x o The highly cherty, -thin-bedded dolomite strata of Lower Silurian (Alexandrian) age are exposed in the cut at the top of the highway grade. Small fossils are rather sparsely present in the chert as well as -the "honey-comb" coral, Pavo sites . The top of the Lower Silurian ledges lies at about 800 feet, reflecting the slow rise of the strata to the north, be-tween Stops 3 and 5. This northward rise of the rock layers continues far into Wisconsin, so that farther north the Galena dolomite again comes to the surface and eventu- ally the ancient Pre-Cambrian "granite basement" is exposed. 0.0 9.5 Continue ahead (N) on Route 78. - 4 - 2.9 12.4 PLEASANT VALLEY. 1.1 1-3.5 Town Hall on right. 1.0 14.5 Turn left (W) on side road and cross Plum River ("lest Branch). 1.1 15.6 Turn left (W) at school house in ED.IOVILLE. 1.5 17.1 Forks. Go right on road marked "Massbach" . 1.5 18.6 Montrose School on left. 0.5 19.1 Intersection. STOP NO. 6. Remain in cars. Between -the school house and the intersection, route travels over ridge summit at an elevation above 1020 feet. Because all of the country within view is part of "the un- glaciated area, it preserves the appearance which much of Illinois had before the coming of the glaciers. The region is in the mature stage of the erosion cycle; that is, it is well drained, in a dendritic pattern, and the area of the ridge tops about equals the area of the valleys. Although the region is dissected to a rough, hilly terrain as a result of stream erosion, the ridges all rise to about the same height, to produce a level horizon. The 1000 foot ridge top level is the remnant of a former peneplain. This wes a plain of erosion developed at a time in the past when the region lay close to sea level and the streams could no longer deepen their valleys. Their activity, confined to latera? cutting, eventually reduced all of the region to a nearly level plain. Later, perhaps not long before the Ice Age (Pleistocene), the region rose many hundreds of feet and the streams were once again able to resume downward cutting, to produce the rough country we see today. If sea level does not change in the interim, a new peneplain will in time develop at or below -the level of the present valley floors. 0.0 19.1 Turn J-tfft (NE) at intersection. Route is through picturesque Driftless Area country back to Route 78 and Stockton. 2.6 21.7 STOP NO. 7. Remain in cars. The splendid view to the northwest overlooks the Apple River country, in the direction of Charles Mound, the highest point in Illinois (1241* )• We are standing on the northwest edge of the Silurian escarpment, beyond which erosion has removed the Silurian rocks, except for isolated remnants, called "outliers". Cnce the outliers were connected with the parent escarpment and the Silurian dolomite existed as a continuous formation over all of no rthwe stern Illinois. The low lands, between the outliers, are floored with Ordovician, Galena Dolomite, the same formation seen at stops 1 and 2, far to the south. Were it not for the structural uplift along the Savanna-Mt. Carroll-Lanark anticline, the Galena would not be again exposed south of the area now in view. 2.0 23.7 Road intersection. Turn left (N). — - 5 - 1.0 24.7 Road end. Turn right (E) at Stockton Center School. 1.1 25.8 Road intersection; continue ahead (E). 0.5 26.3 DANGER. Stop sign. Turn left (N) on Route 78. 1.2 27.5 Enter STOCKTON. 0.5 28.0 Park on east side of highway, north of Standard Filling Station in Stockton. LUNCH STOP. Reassemble at this point in one hour. 0.0 28.0 Drive to -right around block and return south through Stockton on Route 78. 0.5 28.5 Leave Stockton. 1.4 29.9 Galena dolomite outcrop on left. 4.0 33.9 Cross Plum River. 2.7 36.6 Turn left (NE) at Pleasant Valley Town Hall. 2.8 39.4 Intersection at School House; oontinue ahead (NE). 2.7 42.1 Intersection at Willow School; continue ahead (E) on minor road. 0.5 42.6 Road is floored by ledges of Lower Silurian, Kankakee dolomite. Bare rock on ridge tops indicates unglaciated area, as does splendid view of summit peneplain and maturely dissected terrain. 0.6 43.2 Side road from right; continue ahead (E). 0#6 43.8 Road intersection; continue ahead (E). 0.7 44.5 Road turns right (S), 0.2 44.7 Road turns left (E) . 0.2 44.9 Forks; go right; road travels over white chert in red clay, a result of the residual weathering of the cherty Kenkakee dolomite. Road turns left (E) and descends hill. 0.3 45.2 June ti on with main road from left; continue ahead (E). 0.2 45.4 Turn right (S) just short of bridge. 2.2 47.6 Church and cemetary. Turn left (E) and join blacktop 0.4 48.1 Bridge over East Plum River. STOP NO. 8. Remain in cars. The ledges in the creek just north of the bridge represent the top (Dubuque Member) of the Galena Formation. By comparison with the level water surface, it can be seen that the strata incline slightly to the south. This dip causes the Galena to disappear beneath the floor of the valley south of here, and to not reappear until brought to the surface by the uplift at Mt. Carroll. - 6 - O.Q 48.1 Continue ahead (E) up grade. 0.3 48.3 STOP HO. 9. Park along roadside. In the right hand road ditch and cut, blue sha'.e with thin-bedded lime- stone is exposed. Some limestone layers are c- v^red with brachiopod shells, bryozoa (see appendix plate) and other fossils. Similar fossils occur free in the shale. The fossils 'cm the nature of the rock indicate it to belong to -the Brainerd (uppermost; member of the Maquoketa formation. This shale formation of late Ordovician age, 1 .es between the hard dolomites of the Galena below and the Silurian (Edgewood, Kankakee, and Hopkinton) above. Because it is weak, it tends to make gentle slopes between the upper and lower dolomite escarpments. Although the formation has been crossed numerous times during our itinerary, this is the first place at which it\vas found to be exposed. Even such exposures tend to be transient. 0.0 48.3 Continue ahead (E) and ascend grade to ridge summit, capped by Silurian dolomite. 3.6 51.9 DANGER. Stop sign. Turn right (S) on Route No. 73. 3.5 55.4 Along creek to left, Maquoketa Shale is exposed in creek bed and basal layers of Silurian limestone in creek bank. (Ordovician-Silurian contact about 810') 2.7 58.1 DANGER. Stop sign. Continue ahead on Route No. 72. 1.0 59.1 Turn right into quarry. STOP NO. 10. Quarry in Niagaran, Hopkinton Dolomite. Here as at Stop No. 3| we find the upper Pentamerus band (low in the quarry), upon which rests the Cerioni tes bed, The latter is here much more f ossilifero than at No. 3 and has, in addition to Cerioni tes dactyloides, numerous brachiopods (Pe ntam erus maquo keta, Lepta ena rho mboi dalis, Airy pa reticu laris , etc . ') , as well as gastropod!; ("snails ) and other mollusks. The organ pipe coral ( Syringopora ) occurs as casts of the tubules, in both beds. The upper Pentam erus o blon gus band is 8 feet thick and splendid large specimens are found at its base. The Cerio ni tes beds are 12 feet thick and are overlain by rough weathering strata full of Fav osites (Honey Comb coral) Halysites (Chain coral), and other corals. At least 13 feet of these coralline strata are exposed. Similar coral beds overlie the Cerioni tes zone in Iowa, and are found in northeastern Wisconsin (Upper Coral Beds), upper Michigan (Cordell Formation) and on Manitoulin Island in Lake Huron. It is by means of the recognition of similar successions of fossils zones that geologists are able to determine the contemporaneity of formations over widely separated regions. - 7 - From the point at which we turned south onto Route 73, the rock layers have shown a steady but very gentle southward descent. However two miles southwest of the quarry, Galena dolomite crops out along a creek at about the same elevation as we are here (850'). This represents an uplift of over 300 feet in so short a distance, and a return to the Savanna-Mt. Carroll-Lanark uplift on which the trip began. End of Conference To return to Mt. Carroll via Routes 52-64, go south 3-1/4 miles through Lanark on Route 72 and turn right (W) . To go to U. S. Route 20, Galena, Freeport, and Rockford, turn north on Route 72. - 8 - GEOLOGICAL HISTORY OF MOUNT CARROLL AREA DEEPLY BURIED FORMATIONS The oldest bedrock strata known to come to the surface in the Mt. Carroll area belong to the Prosser Dolomite Member, Galena Formation, of Ordovician Age. A deep water well drilled at Savanna shows that older dolomite, sandstone and shale of Ordovician Age lie below the Galena Dolomite here (see well record in appendix), and that still older Cambrian strata lie below -the Ordovician rocks. From evidence of deep wells in other parts of Illinois, and from studies in Missouri, Wisconsin and Minnesota, we know that below the stratified Cambrian sandstone, limestone and shale is rock of quite a different nature which, for convenience, we here refer to us the granite basement of Pre-Cambrian age. PRE-CAMBRIAN BASEMENT Actually this basement or foundation, upon which the stratified deposits of the ancient Paleozoic seas were laid down, has had a long, complex and violent history. It involves the first three- fourths of all geologic time (roughly 2 4 000,000,000 years). During this time, high mountain ranges were upraised, molten rock matter was injected into the strata deep in the crust or spewed out on the surface as lava, the stratified rocks were -twisted, shattered and partly remelted, and between these periods of violence, the forces of erosion had time to wear the mountains to nearly level plains. These periods of erosion and of mountain building (dias trophism) alternated several times during the billion and one-half years of Fre-Combrian time, terminating with a final period of erosion that carved the level peneplain of the "granite basement" surface. The rocks which make up this foundation are all of hard crystalline types. Some, such as granite, gabbro, porphyry and basalt, cooled from a molten state, either deep below the surface (intrusions) or as lava out- pourings (extrusions) , Sedimentary rocks which were originally shale, limestone or marble were transformed by heat and stress into "metamorphic" rocks like gneiss, schist, marble and quartzite. PALEOZOIC SEAS The long period of erosion and peneplanation that closed pre- Cambrian time came to an end when the Cambrian seas spread over the region some 500,000,000 years ago to begin the deposition of the layered bedrock formations. Similar seas persisted here through most of Paleozoic time. Thus the marine deposits of the Cambrian, Ordovician and Silurian periods are still to be found in the Savanna region,, The Devonian lime- stones were certainly once present but have been removed by erosion, and Mississippian and Pennsylvanian strata may also once have existed here. The teeming life of some of these ancient Paleozoic seas is amply attested by rich fossil beds, such as visited on this trip. - 9 - LONG INTERVAL OF EROSION After the last of the Paleozoic seas left this region, it was uplifted a moderate distance above sea level; and so it has remained ever since* Thus, during the Hesozoic days of the dinosaurs and during all Tertiary- time that followed (a time span totalling about 250,000,000 years), weathering penetrated deep into 'the bedrock, and streams carved the landscape into a pattern of valleys and ridges. At times the whole region would be reduced to base level. Such a condition arises when the land surface has been cut down to a near- plain close to the level of the sea. It seems to have taken place at least -twice during the long-time span between the Carboniferous and the Ice age, as indicated by erosional terraces on the present uplands. The higher of these terraces, the Dodgeville peneplain, is not preserved in the Mt. Carroll ares, but the lower, or Lancaster, level bevels the flat ridge tops of the Carroll County uplands. It is believed to have developed in the latter part of the Tertiary period, before the coming of the continental glaciers. Because the region was eroding and the detritus was being carried off to be deposited elsewhere, no strata of Mesozoic or Tertiary age are known from the Savanna area. GLACIAL PERIOD The next deposits to be laid down in the region, following the long interval of erosion, accumulated as a result of the glacial invasions which began about a million years ago. Of the four main continental glacial advances of the Pleistocene period, only the third, or Illinoian, entered the Mount Carroll area. This ice mass spread southward and westward from a center of accumulation east of Hudson Bay. It covered nearly all of Illinois, but in the northwest, stopped along a line running from south of Savanna to just west of Mount Carroll and just east of Stockton. In addition to the glacial till and water laid glacial deposits, there was laid down over the uplands a blanket of fine silt, called loess. This was dust picked up by the Ice Age gales along the alluvial flats of great rivers like the Mississippi and dropped over the uplands. The deposits are thick close to the Mississippi, as near Savanna, and thin rapidly away from the river. Today streams continue to deposit alluvium over their flood plains and man, in his agriculture and his engineering speeds the unceasing erosive activity of Nature. For further information, consult: "Physiographic Divisions of Illinois," Leigh ton, Ekblaw & Horberg, Report of Investigations No. 129, Illinois State Geological Survey ■ "Bedrock Topography of Illinois," Horberg, Bulletin No. 73, Illinois State Geological Survey. "Geology of the Galena and Elizabeth Quadrangles," A. C. Trowbridge, Bulletin No. 26, Illinois State Geological Survey. GENERALIZED GEOLOGIC COLUMN FOR MOUNT CARROLL AREA ERAS PERIODS Cm ca OH aj © e hoe -•J (a <+H © O rH © £ CO w -P 3 aj •r) r-i •H a, O © M -H Quaternary Tertiary Cretaceous Jurassic Triassic Permian Pennsylvanian Mississippian Devonian Silurian © -P u •g +» it © & M «h O © Ordovician EPOCHS REMARKS 10 KJ&VLftlUUS -+ J.. Cambrian Pleistocene Pliocene Miocene Oligocene Eocene Paleocene Peorian Loess. Illinoian glacial drift. I . Al luvium in jr iver valleys . i Not present in Carroll ' County. i ! .' t . .. _ Present only in extreme southern.Illinqis.^ Not present in Illinois. | Not present in Illinois. Not present in Illinois. Not present in Carroll j County. ........ j Not present in Carroll LjCounty* - ... .„..__ I Not present in Carroll County. Cayjigan Niagaran ij Not present in this area. .„. _ Pentamerus Beds Coral Beds j Stricklandia bed I Kankakee cherty beds. .i.Edgewpo.d earthy dolomite,. Maquoketa shale and shaly limestone. Galena dolomite-in outcrop Decorah shale ) Flatteville Is. )in wells : Glenwood Is. ) Chazyan St. Peter ss. - in wells. j Shakopee dolomite) Prairie du Chien New Richmond ss. )in wells Oneota dolomite ) Alexandrian fc~. : \ Cincinnati an Mohawkian -t roterozoic rcheosoic Referred to as "Pre-Cambrian" time. In deep wells only. No data available. BURIED FORMATIONS - CARROLL COUNTY Surface 610' above sea level. "TKT Dolomite overlain by 5 T of soil. Shaly beds in lower 100 feet and sandy near bottom. . — . ] H. Shale and s andy dp lomi te J S* Loose, clean sand. "" ? " — 1 <" ' "" """ " ""' "" "",. "J | Dolomite shaly and sandy at top. \JL L J I Lower z/z very cherty: -.—; ■■ ;."- | Bottom sandy and ' „ oolitic. .jL.. ^ "• - ' -■ • — -•"■ to X ^'.!o " «o T. r-t O p- ~r \ — Dolomite, some pink and red layers . GALENA - PLATTEVILLE GLENW0qD___ _ ST. PETER_ ONEOTA - SHAKOPEE Fine glauconitic sand and sandy shale. vrf """ ~~ " — — o Sandstone, coarse to medium; some dolomite j Fine sandstone, ♦I shale, some dolomite, §! glauconitic^ JJ TREMPEALEAU FRANCONIA IRONTON - GALESVILLE EAU CLAIRE ... ! Q O M « % M i " i > ! S ■ « . o O I M © Si Dep-th 1308», or 698' below sea level. Generalized from Savanna City deep water well, drilled, 1935, at Pine and Barren Sts. Time Table of Pleistocene Glaciation (after M, 1.1. Leighton and H» B. Willman, 19^0) :ages Sub-stages Nature of Deposits Special Features 5 cent Soil, infant to youthful pro- file of weathering, lake and river deposits, dunes, peat„ .sconsin *th glacial) Late Mankato Early Cary Tazewell Iowan Farradale (Pro-Wis.) Fluvial deposition - Mississippi, Illinois, and Ohio river valleys j dune sand, some loess deposits along Missis sippi River Valley; and deposits in Lake Chicago, Drift, loess, dunes, beginning of deposits in Lake Chicago Drift, loess, dunes, lake deposits. Drift, loess, dunes Loess (in advance of glacia- tion) Lake Agassiz Torrent eroded Late Mankato deposits Lake Duluth Torrent eroded F,arly Mankato deposits Forest bed, Two Creeks, Wisconsin Kankakee and Lake Maumee Torrents Fox River Torrent Westward diversion of Mississippi River into Iowa by Tazewell ice lobe ingamon ird inter glac ial) Soil, mature profile of weath- ering, alluvium, peat .linoian ird glacial) Buffalo Hart Jacksonville Payson (terminal) Loveland (Pro-Ill. ) Drift Drift Drift Loess (in advance of glacia- tion) irmouth !nd interglac: Lai) Soil, mature profile of weath- ering, alluvium, peat. insan nd glacial) Drift Loess 'tonian .st interglac: Lai) Soil, mature profile of weath- ering, alluvium, peat. .braskan .st glacial) Drift TILL PLAINS SECTION, GREAT LAKE SECTION CENTRAL LOWLAND PROVINCE OZARK PLATEAUS PROVINCE CENTRAL LOWLAND PROVINCE INTERIOR LOW PLATEAUS PROVINCE ILLINOIS STATE GEOLOGICAL SURVEY COASTAL PLAIN PROVINCE PHYSIOGRAPHIC DIVISIONS OF ILLINOIS (Reprinted from Report of Investigations No. 129, Physiographic Divisions of Illinois, by M. M. Leighton, George E. Ekblaw, and Leland Horberg) I (71328) COMMON TYPES of ILLINOIS FOSSILS Plate Cup coral GRAPTOLITE Lithostrotion CORALS Honeycomb coral CRINOID *#§|^ PENTREMITE Fenestella Archimedes Branching BRYOZOA ingula Orbiculoidea Spiriferoid Productoid Pentameroid BRACHIOPODS Plate 2 Common Types of Illinois Fossils "Clam" "Scallop" PELECYPODS Curved cone Coiled cone (Nautilus) Straight cone CEPHALOPODS Low - spired High- spired Flat - spired GASTROPODS Bumastus Calymene (coiled ) OSTRACODS (greatly enlarged) Calymene (flat) TRILOBITES 5S*"