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Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 University of Illinois Urbana-Champaign 
 
 http://archive.org/details/earthhistoryfiel1948illi 
 
/ e^ii//^ 
 
 Earth History Field Trip 
 for High School Science Teachers 
 Stockton, Illinois. May 15, 1948 
 
 Sponsored by State Geological Survey 
 M. M. height on, Chief 
 Gilbert 0. Raasch, Coni'orence Director 
 Principal II. R. Holloway, Conference Host 
 
 General Instructions: 
 
 1. Please be prepared to leave promptly at 9:00 a.m., Central Standard Time. 
 
 2. Cars will assemble at Stockton High School. 
 
 3. Participants will provide themselves with lunches before starting. 
 
 4. At scheduled stops, please assemble promptly near leader to hear his dis- 
 cussion before scattering for individual examination of points of interest; also 
 please be prompt to leave upon signal. This is especially desirable if the group 
 is large. 
 
 Instructions for Car Drivers: 
 
 To expedite the trip and for safety, please 
 
 1. Identify your car by attaching one of the tags provided. 
 
 2. Have your car in line before the trip starts. 
 
 3. Follow carefully and keep fairly close to the car ahead, with due regard 
 to safety. 
 
 4. Keep all gaps in the caravan closed, especially while traveling through 
 the city, in order to prevent other cars from inserting themselves in the caravan 
 or crossing the caravan at intersections. 
 
 5. Watch the cars ahead and behind for signals. 
 
 6. Keep your place in the caravan as far as possible; do not attempt to pass 
 ahead of any in the caravan unless they drop out of line, nor to gain an advanced 
 position at stops. 
 
 7. If for accident or other reason you drop out of line, let those following 
 you proceed, except for such help as may bee needed; in case of accident to the 
 rear car of the caravan, signal those ahead. 
 
 8. Any car dropping out of line shall take up the rear when rejoining the 
 caravan. 
 
 9. When parking in line at stops, draw close to the car ahead; when parking 
 parallel, do not leave unnecessary space between cars. 
 
 10. One passenger in each car, preferably sitting beside the driver, should 
 read the itinerary and keep the driver adequately informed with regard to stops, 
 turns, etc. . 
 
-2 ■• 
 
 ?AaT II - ITINERARY 
 0.0 Caravan assembles facing south on y/est side of street in front of school. 
 
 0.1 Turn right (W) two blocks. 
 
 0.2 Turn right (N) . 
 
 0.4 Park below city reservoir. 
 
 STOP I. Go to top of hill at reservoir. Elevation here is 1112 feet above 
 sea level. Knob to west is capped by -Silurian Dolomite but reservoir hill 
 is capped by dolomite layer slightly lower down, in Ordovician, Maquoketa 
 Formation. Fossils of Maquoketa age are present. 
 
 View west is across upland of Ordovician, Maquoketa shale, which is 
 dissected by steep-sided valleys that cut down into Ordovician, Galena 
 Dolomite (see Geologic column). To south, line of high hills is Silurian 
 ("Niagara") Escarpment. To north in foreground is Benton Mound, an out- 
 lier of Silurian Dolomite left behind when the escarpment retreated south- 
 ward under the action of erosion. 
 
 Reservoir Hill is outside the limit of glaciation. During the Illinoian 
 Stage of glaciation, the continental ice sheet stood just to the east, and 
 the ice front extended in a fairly straight line north and south from 
 Stockton. The extent of the ice sheet can be traced today by the presence 
 of pebbles and boulders of rock types foreign to the region, some of them 
 carried down by the ice mass from as far north as Canada.. 
 
 0.4 Turn right (E) . 
 
 0.6 Main St. Turn left (ll) . 
 
 0*8 Turn right (E) on Summit Ave. 
 
 0.9 STOP II. House excavation exposed yellow till of Illinoian glaciation, 
 
 leached and weathered, with some pebbles of igneous and metamorphic rocks 
 which do not outcrop south of the Lake Superior Region and Ontario. Till 
 is unsorted glacial material, ranging in size from fine clay to large 
 boulders. This material was left behind when the glacier melted away. 
 
 1.1 Turn left (H). ■ 
 
 1.2 Caution. Cross U. S. Highway No. 20, and continue ahead (N) • For 3 miles, 
 
 route passes along edge of glaciated area, but the valley of the creek to 
 the west is outside the glacial limit. This creek once carried the 
 waters from the melting ice. 
 
 4.4 Turn left (w) • 
 
 5.5 STOP III. Quarry in Ordovician, Galena Dolomite, This is high in the 
 
 Galena Formation and is the Stewartville Member, characterized by lack of 
 chert and moderately thick, even layers. Moulds of fossil shells, chiefly 
 gastropods ("snails") occur sparsely. The rock is being quarried for 
 agricultural limestone and for road macadam, 
 
 6.5-6.6 Road jogs left, then right. 
 
 7.0 STOP TV. Kill rising above road to south is north end of Benton Mound, here 
 1180 feet high, (1/2 mile SE it rises above 1220 feet) It is capped by 
 
 Silurian Dolomite, 
 
To north wo look dewn on a very flat upland cut in the Maquoketa Shale - 
 This upland was once the divide between streams which drained into the 
 Pecatonica to the east and streams v/hich drained directly into the 
 Mississippi to the west. 
 
 However, when the Illinoian Glacier stood just 2 l/2 miles east of here, 
 it blocked the eastward flowing streams. First, they backed up and formed 
 a lake in the valley to the right. Eventually this lake filled and spilled 
 over the divide into the westward flowing streams. This outlet was along 
 the present course of Apple River Canyon which was cut 200 feet deep, down 
 through solid rock by these glacial torrents. That is why the South Fork 
 of Apple River, which once flowed Southeast, today flows Northwest. 
 
 7,1 Turn right (N) and go north to Apple River State Park, 
 
 10.5 Enter Apple River State Park, Road descends from Maquoketa Upland through 
 ravine cut in Galena Dolomite . 
 
 10,7 STOP V, Apple River Parking Area, "Walk west to foot bridge, cross Apple 
 River, and take trail ascending bluff. Cliffs are in Galena Dolomite, 
 Near summit of trail it is easy to trace the original valley which flowed 
 southeast and is now occupied by North Fork on the left and by South Fork 
 on the right, When the Illinoian Ice Sheet dammed South Fork near Stock- 
 ton, the waters cut their way to the Mississippi by carving out the deep 
 canyon. Go to top of bluff and a short distance south to observe the 
 canyon's depth. It is 200 feet deep, nearly straight in a NE-SW direction, 
 and over 4 miles long. Except at its upper and lower ends it is 
 inaccessible except on foot. 
 
 10.7 LUNCH STOP on a,ite of old Millville. 
 
 10.7 Leave parking area, cross bridge, and immediately turn left (W). 
 10,9 Cross North Fork of Apple River and ascend steep hill, 
 
 11.8 Quarry in Stewartville Dolomite of Galena Formation on right. Some layers 
 
 have numerous molds of brachiopod shells. 
 
 12.4 STOP VI. The mound to north is capped by Silurian Dolomite. Road is on 
 
 flat Maquoketa Upland which stretches as a level plateau southeast to 
 Benton Mound. Between ovserver and Benton Mound, the deep canyon of 
 Apple River is hidden from view, except as indicated by projecting tree 
 tops. 
 
 13.0 Turn right (N) . 
 
 14.7 Cross North Fork of Apple River. Note hew much shallower valley is here than 
 in the park. 
 
 16.9 Caution. Junction with County Highway at SE edge of Apple River Village. 
 
 Continue on County Highway and turn left (W) through Apple River. 
 
 18.9 Cross Apple River, here a shallow valley not affected by glacial influences. 
 
 20.5 STOP VII. East end of deep cut of I.C.R.R. Rock from cut has been piled 
 
 along right-of-way to east. 
 
Cut is in about 25 feet of beds from the middle portion of the Maquoketa 
 Shale. These are shales, siltstones, and impure limestones containing 
 fossil trilobites (Isotelus), cephalopods (Orthoceras sociale), gastropods' 
 (Liospira ), graptolites (few), and shiny-shelled brachiopods related to 
 modern TXngula and Piscina , Note definite, even stratification, typical 
 of sediments deposited in quiet water. 
 
 20.8 Turn right (N) and cross R.R. on wooden overpass. 
 
 21.1 Road turns 'left (w) . 
 
 22.7 Road turns left (S). 
 
 22.8 Road junction; turn right (W), 
 
 24.4 STOP VIII, on Charles Mound, which rises to a crest of 1241* a mile W. NW. 
 
 This is less conspicuous than many surrounding hills because it rises from 
 a high plateau of the Maquoketa Formation; the mound is capped by Silurian 
 dolomite. To south, the Silurian (Niagara) Escarpment is clearly shown; 
 higher hills to north are in Wisconsin. 
 
 A short distance down the road to the south (left), blue clays with 
 irregular layers of limestone full of fossils are present in road ditch. 
 These beds lie near the top of the Maquoketa Formation. Flat brachiopod 
 shells (Rafinesquina and Strophomena) are most conspicuous. 
 
 24.4 Turn left (S). 
 
 25.2 Turn right (W). 
 26.2 Turn left (S ) . 
 
 26.7 Road turns right (71) . 
 
 27 # 3 Turn left (S) and enter Scales Mound Village. 
 
 27.6 Cross overpass over I.C.R.R. 
 
 27.6 STOP IX. Park South of overpass along main street. Walk west along R.R. 
 tracks to deep rock cut. Here may be seen the contact between dark gray 
 shale of Maquoketa Formation above and rough-weathering buff dolomite of 
 the Galena Formation below. Immediately above the dolomite and again a 
 foot higher may be seen two soft rusty bands. These contain tiny pelecy- 
 pods or clams (Ctenodonta fecunda) and snails (Liospira Micula) not found 
 at any other stratigraphic level in the region. Because of these dwarf 
 fossil shells, geologists refer to these beds as the "depauperate zone." 
 Graptolites, an extinct group of sea animals supposedly related to corals, 
 are said to occur in the shale above the "depauperate zone." 
 Note how rock grades upward into residual soil. 
 
 27.6 Continue ahead (S). 
 
 2G.3 Turn right (Vl) at highway junction. 
 
 28,6 Outcrop in roadcut is silty dolomite of Maquoketa Formation. 
 
• - 
 
 ' ~ .4 STOP XI, at highway junction. Ascend Scales Mound. Highest rock on mound 
 is cherty Silurian Dolomite of Kankakee Formation. Numerous small marine 
 fossils and the honeycomb coral Favosites occur in this rock. 
 
 Note how huge blocks of the dolomite have slumped down the sides of the 
 bluff due to the weathering away of the soft Maquoketa Shale which under- 
 lies the dolomite (the same blue shale zone as seen at Charles Mound), 
 
 On a clear day, a remarkable view of the surrounding region can be 
 gained from this point. Once again, the Silurian Escarpment is near at 
 hand to the south. Far to the west, across the Mississippi River in Iowa, 
 the escarpment can be seen holding a southeast-northwest alinement. Scales 
 Mound is an outlier of this Silurian (Niagara) Escarpment. Other famous' 
 outliers may be seen, such as Sinsinawa Mound many miles nearly due west, 
 across the Wisconsin line; also far to the north, the Platte Mounds, 1420 
 feet high and 20 miles away, The most famous outlier of all, the norther- 
 most and highest (1716 feet), Blue Mounds lies northeast beyond the 
 Wisconsin horizon. These outliers tell us that the Silurian sea extended 
 far beyond the present Silurian escarpment. 
 
 In the near distance, to the west, the Maquoketa upland is broken by 
 valleys deeply cut down into the Galena Dolomite, which here bears rich 
 deposits of lead and zinc ore. 
 
 The day f s conference clearly shows how the bedrock controls the topo- 
 graphy of the region, with the Galena and Silurian Dolomites making steep 
 slopes or cliffs and the softer, shaly Maquoketa Formation, making nearly 
 flat broad terraces. Throughout the region, however, the highest hills, 
 regardless of the rock composing them, all rise from 1100 to 1200 feet 
 high. These crests are believed to be remnants of what was once a con- 
 tinuous plain (or peneplain) formed when the region lay about 1000 feet 
 lower than it does today. At that time, long-acting erosion had cut away 
 still higher hills and reduced the region to this plain surface. Later, 
 the region was again uplifted and erosion is actively cutting it down 
 and dissecting it into a maze of narrow ridges and deep_ valleys. If 
 nothing intervenes, in time a new peneplain will be formed, but little 
 above the level of the Mississippi, 
 
 This region preserves this long erosional history because it was never 
 covered by glacial ice, which left a thick blanket of glacial drift over 
 most of the rest of Illinois. This unglaciated region, entirely sur- 
 rounded by glaciated country is world-famous as "The Driftless Area," 
 
 END OF CONFERENCE - BON VOYAGE] 
 
 Note: The left fork at the base of the mound continues SW for 3 miles as a 
 
 beautiful "skyline drive" and passes through attractive country to Galena, 
 
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 GE^RALISroGEOpfilC.gOLTOCEO^E^pffl.JO^AYIKS^COWTY 
 
 ERAS 
 
 PERIODS 
 
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 Mesozoic 
 "Middle Life" 
 (Age of Reptiles) 
 
 Quaternary 
 
 Tertiary 
 
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 bO 
 
 Cretaceous 
 
 Jurassic 
 
 Triassic 
 
 Permian 
 
 Pennsylvania!! 
 
 Mississippi an 
 
 Devonian 
 
 Silurian 
 
 Ordovician 
 
 Cambrian 
 
 Proterozoic 
 Archeozoic 
 
 ~~\ 
 
 EPOCHS 
 
 Pleistocene 
 
 Pleiocene 
 
 Miocene 
 
 Oligocene 
 
 Eocene 
 
 Faleocene 
 
 Cayugan 
 
 Hi agar an 
 
 Alexandrian 
 
 Cincinnatian 
 
 Mohawkian 
 
 Chazyan 
 
 REMARKS 
 
 Illinoian glacial drift 
 along east edge of county. 
 Loess deposits on upland & 
 alluvium in river valleys. 
 
 Not present in Jo Daviess 
 County. 
 
 Present only in extreme 
 southern Illinois. 
 
 Not present in Illinois. 
 
 Not present in Illinois. 
 
 Not present in Illinois. 
 
 Not present in Jo Daviess 
 County. 
 
 Not present in Jo Daviess 
 County. 
 
 Not present in Jo Daviess 
 County. 
 
 Not present in this area. 
 
 present only on highest 
 mounds south and west of 
 trip area. 
 
 Kankakee cherty dolomite 
 Edgewood thin-bedded earthy 
 dolomite » 
 
 Maquoketa shale and shaly 
 limestone . * 
 
 Prairie du Chien 
 
 Galena dolomite - in outcrop 
 
 Decorah shale A 
 Platteville Is. rin wells 
 Glenwood ss, , _J 
 
 St. P eter ss. - in wells. 
 
 Shako pee dolomite J 
 
 New Richmond ss. >- in wells 
 
 Oneota dolomite _.' 
 
 V-Referred to as "Pre -Cambrian" 
 time . 
 
 J 
 
 In deep wells only. 
 
 No data available. 
 
 May, 1948 R.W.E. 
 
- 6 ■ - 
 
 PART IV 
 GEOLOGICAL HISTORY OF APPLE RIVER AREA 
 
 DEEPLY BURIED FORMATIONS 
 
 The oldest bedrock that comes tc the surface in eastern Jo Daviess County 
 is the Galena Dolomite of Ordovician Age (see geologic column, Part III). Deep 
 wells drilled over 1500 feet deep at Galena and nearly 1300 feet deep at Stockton 
 show older rocks lying at lower levels. Beneath the Galena Dolomite, lies the 
 Platteville Limestone, underlain by the St. Peter Sandstone, that in turn by the 
 Prairie du Chi en Formation. All these are still of Ordovician Age, but older 
 than the Galena. They come to the surface farther north in Wisconsin and east 
 in Central Illinois. 
 
 Beneath these older Ordovician rocks are still older layers of sandstone 
 and dolomite over 1000 feet thick that belong to the Cambrian Period. Wells in 
 Jo Daviess County do not penetrate below the Cambrian strata, but in adjoining 
 regions crystalline rocks such as granite, basalt, or gniess and/or dark red 
 sandstones of Pre-Cambrian age are present. These oldest rocks of all are 
 deeply buried everywhere in Illinois but come to the surface in Central Wisconsin 
 and northward to the region of Hudson Bay. 
 
 EXPOSED FORMATIONS - Galena Dolomite. 
 
 A dolomite is a limestone having a part of the usual calcium replaced by 
 magnesium. Nearly 250 feet of such rock is present in the area, and this thick- 
 ness can be subdivided into several members which have been given geographic 
 names. Those exposed in the field trip area are, from top downward, as follows: 
 
 Dubuque Member 
 Stewartville Member 
 Prosser Member, 
 
 The uppermost or Dubuque Member is about 30 feet thick and characterized 
 by thin bedding, with dolomite layers separated by shaly layers. Fossils are 
 rather common, notably a Lingula-like brachiopod, Lingulasma iowensis. 
 
 Below the Dubuque Member a somewhat greater thickness of thicker bedded, 
 bluish gray, buff weathering dolomite without chert is characterized by several 
 species of large gastropods (snails). This is the Stewartville Member. 
 
 The main mass of the Galena Formation (Prosser Member) is a thick-bedded 
 unit of dolomite layers some of which bear abundant white chert. There are two 
 zones of the large and striking "sun-flower coral" which is really an archaic 
 type of sponge called Receptaculites oweni. The Prosser dolomite weathers into 
 rough ledges and breaks down under weathering agencies to a dolomite sand. 
 Because of its ready solubility, this unit is the rock in which many caves have 
 been formed in adjoining areas. 
 
 The Galena Formation is important in the western part of the county and 
 in adjoining parts of Wisconsin and Iowa for the valuable lead and zinc deposits 
 which it contains. These are not discussed at this time, as the present trip 
 does not include the mining region. 
 
« 7 - «. 
 MaQ/uoksta Formation 
 
 Above the Galena Dolomite lies an irregular thickness of shale and shaly 
 limestone, the Maquoketa Formation^, Like the Galena Formation, the Maquoketa 
 can be subdivided into anumber of members, but these subdivisions have not yet 
 been published for the area. The lower part of the formation is a soft, dark 
 shale with one or more layers of rusty punky shale full of minute mollusks and 
 phosphate pellets. The middle part of the formation is made up of thin layers 
 of earthy brown dolomite and tan to dark gray shale. Fossil trilobites, phos- 
 phatic shelled brachopods and other fossils occur here. The upper part of the 
 formation is mainly soft blue clay with irregular thin limestone bands jammed 
 with fossil brachiopods and bryozoa. 
 
 Sometimes this upper zone is thin or missing because of erosion which took 
 place after the shale was deposited but before the next overlying Silurian dolo- 
 mites were laid down. This is evidence of a land interval between the time when 
 the sea withdrew after depositing the Maquoketa shale and reappeared again in 
 Silurian Time, 
 
 Hundreds of feet of Silurian dolomite were deposited over all of northern 
 Illinois, but in the Apple River area most of this dolomite has been stripped 
 away by erosion since that time. Today only thin remnants of the lower part of 
 this dolomite remain as cap rock on the higher hills. 
 
 The lower 50 feet of the Silurian Dolomite can be divided into two 
 formations, the Edgewood Member below and the Kankakee above. The Edgewood fills 
 irregularities in the uneven top of the Maquoketa Formation, and therefore varies 
 a good deal as to character and thickness. Where seen on the trip it is thin- 
 bedded, almost shaly and without chert. The overlying Kankakee has somewhat 
 thicker beds, without shale, and full of chert in white bands containing the 
 coral Favosites and numerous other small fossils. 
 
 EARLY GEOLOGIC HISTORY 
 
 After Pre-Cambrian time, when the most ancient "basement" rocks were 
 formed, folded, and then worn down to a nearly level plain, the Apple River area 
 was aLmost continuously covered by the waters of inland seas down through the 
 later part of the Cambrian, the Ordovician, much of the Silurian, and a part of 
 the Devonian periods. There is even possibility that the Mississippian and 
 Pennsylvanian seas, so prominent farther south in the State, extended over this 
 area, - but here evidence is lacking, 
 
 0m the other hand, since Pennsylvanian time at least, there is no reason 
 to believe that the sea ever returned to this area, which remained dry land at 
 moderate elevations above the sea. Except for a broad, gentle arching which 
 took place before Pennsylvanian time and had its apex in central Wisconsin, the 
 rock layers were at no time seriously disturbed. Through the hundreds of 
 millions of years which make up Mesozoic and Tertiary time, weathering by the 
 atmosphere and erosion by streams have combined to wear away many hundreds of 
 feet of strata which once overlay this region. It is these forces that carved 
 the landscape to its present pattern of hills and ridges. In the course of this 
 wearing down, the harder Galena and Silurian dolomites resisted erosion more 
 successfully than did the intervening Maquoketa shales. Therefore, the two 
 
dolomites form cliffs or steep slopes, while the shales form broad gently rolling 
 terraces, Where limestone layers are present in the Maquoketa Formation, they 
 tend to form small knolls as a result of the protection of this limestone 
 cap-rock, 
 
 ICE AGE HISTORY 
 
 During the Ice Age (Pleistocene), continental glaciers descended from 
 northern Canada across northern United States, not once, but four times. 
 Between these periods of glaciation were intervals of mild climate lasting from 
 one to several hundred thousand years. During these intervals, the ice melted 
 away, vegetation flourished and formed soils, and strange or foreign animals 
 roamed the landscape. 
 
 Beginning with the earliest, the four glacial divisions of the Pleistocene 
 are as follows: Nebraskan, Kan s an, Illinoian, Wisconsin. 
 
 Most of Jo Daviess County was never glaciated at all. Yet go any direction 
 from the County, and you will sooner or later pass into glaciated country. This 
 is because Jo Daviess County is part of the famous "Driftless Area," the bulk 
 of which lies to the north, in southwestern Wisconsin. 
 
 This Driftless Area is rather an accidental gap in the glacial coverage of 
 the four stages of glaciation. Two of the continental glaciers, the earliest or 
 Nebraskan and the latest or Wisconsin never reached the boundaries of the county. 
 The Kansan Glacier, advancing from the northwest, barely touched the west edge 
 of the" county, whereas the Illinoian Glacier, advancing from the northeast, 
 stopped a few miles inside the eastern border of the county. 
 
 The prominent physiographic features such as moraines, kames, eskers, etc., 
 generally associated with glacial deposits are not apparent in this region. The 
 glacial till dropped by the melting of the Illinoian Ice Sheet is rather similar 
 in superficial appearance to the normal residual soils of the region, except for 
 the fact that it contains some pebbles of crystalline rocks which must have been 
 carried down from the far north. This suggests that the glacier did not erode 
 deeply in the Apple River area, but limited its activity to a scaping of the 
 locally weathered material from the bedrock surface. This material it spread in 
 an even blanket which reduced the original irregularities of the region, so 
 that today the glaciated area has a much more subdued landscape than that of 
 the rugged driftless area to the west of the glacial limit, 
 
 A special feature of the local glacial geology, the diversion of the head- 
 waters of Apple River and formation of a temporary lake, are discussed in the 
 Itinerary (Part II ) . 
 
 Suggested Reading 
 
 A comprehensive, detailed, and well illustrated account of the geology of 
 Jo Daviess County is presented in Trowbridge and Shaw's "Geology and Geography 
 of the Galena and Elizabeth Quadrangles." This Bulletin No. 26 of the Illinois 
 State Geological Survey (Urbana) is still available for a fee of 50 cents (free 
 to schools). A part of this same- material has also been published by the U. S. 
 Geological Survey as Folio Ho. 200. 
 
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