Bulletin, Issue 37

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University of Illinois, 1919 - Geology

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Page 39 - STRATIGRAPHY dolomite, and thought to represent the residual soil. Above this shale the lower 3 feet or so of the sandstone usually contains a large number of oolitic flints. The following section observed along Pecumsaugan Creek includes the zone of contact with the limestone. Character of strata at the base of the St. Peter sandstone and the top of the Shakopee dolomite along, Pecumsaugan Creek Along Tomahawk Creek near the NW. cor. sec. 35, Dimmick Township (T.
Page 82 - The later Wisconsin gravel of this area is in the main that found within the valleys and is of two sorts, that found in the terraces and that forming part of the valley filling. The former is thought to be of glacial origin in part at least and to have been formed when the ice edge was not far to the east of this region. The gravel forming part of the valley filling is possibly of more recent origin, having been deposited after the Illinois Valley ceased to be the outlet of glacial Lake Chicago....
Page 23 - ... and gradational terraces, flood plains, wash slopes, and alluvial fans, and finally, minor topographic features represented by dunes, hog-backs, and mine dumps. UPLAND PRAIRIES The uplands comprise more than half of the area of the quadrangles, are flat except where crossed by morainic hills, and are largely prairie. The remarkably level character of the intermorainic upland plains is due to the presence of a mantle of nearly flat-surfaced glacial drift. The La Salle quadrangle has the more extensive...
Page 94 - The resulting surface did not have great relief but along the west side of the anticline the surface was possibly 50 to 100 feet lower than to the east of the fold. The dip of the older rocks along the west limb of the anticline was about one-half of what it is at present, and to the east they lay nearly flat; thus the fold had even greater resemblance to a monocline or step fold than it has at present. The pre-Pennsylvanian erosion lasted possibly through the Mississippian epoch and certainly during...
Page 75 - ... soil and peat bed above the Illinoian drift in Sangamon County, Illinois. The Sangamon soil is well exposed in the Hennepin and the La Salle quadrangles (see fig. 25), and it has been noted in many wells and coal borings. It is probably persistent over many square miles especially within the Hennepin quadrangle along lines of interglacial drainage. Where the present valleys have cut down to the level of the floors of the older drainage lines the soil is often exposed. The deposits in this area...
Page 74 - ... QUADRANGLES lying Wisconsin drift. The leached zone of the older till is, in general, thicker than that of the Wisconsin till. Gravel deposits of Illinoian age are not separable lithologically from the later gravels. Exposures of the Illinoian till are very numerous. Along the north and east bluff of Bureau Creek the Illinoian till makes up practically the whole section from where the valley opens into Illinois Valley as far north as the center of Dover Township (T. 17 N., R. 9 E.). Good exposures...
Page 25 - In general, tributary valleys cut into the rock, such as the lower part of Little and Big Vermilion rivers, Pecumsaugan Creek, Cedar Creek, and Clark Run, are narrow and steep sided, some being gorges or canyons. Such valleys are confined to the La Salle quadrangle. Other valleys, especially those in Hennepin quadrangle, FIG. 5. — Profile across a typical valley. but also the upper parts of the valleys in La Salle quadrangle, which are cut into the glacial drift, are broader and have less precipitous...
Page 30 - Feet Feet contact) Shale, gray, with pyrite and coal and white, dolomitic limestone . . Devonian or Silurian system (462 feet) : Limestone, dolomitic, white and gray 34 422 Limestone, grayish white, cherty 13 435 Dolomite, porous, with drusy quartz and chert. . . 85 520 Dolomite, porous, and cavern clay and sand 20 540 Dolomite, porous, with quartz and chert 15 555 Limestone, dolomitic, cream-white, cherty 47 602 Niagaran series: Limestone, dolomitic, straw-colored, porous 6...
Page 45 - Galena-Plattcville as at Split Rock, Deer Park, and Lowell, or fill in the hollows of the eroded irregular surface of the flatlying strata as at the clay pits south of Utica (fig. 15). West of the fold, where the Galena-Platteville group is known only from drilling and where the Galena is overlain by probably the next youngest Ordovician strata in northern Illinois, namely the Maquoketa, the nature of the contact is unknown. That this contact may be marked by a discordance is suggested from the relationships...
Page 100 - SB. corner of sec. 36, Dimmick Township, and was tributary to Tomahawk Creek and Little Vermilion River. It was possibly at this time, if not before, that the Little Vermilion acquired its course across the anticline, as it was probably flowing at a high elevation and on the drift. Another outlet of this lake lay approximately in the position of the present Illinois but the spillway extended somewhat north of the valley so that part of it is preserved in the washed surface exposed in sees. 12, 13,...

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