Bulletin - United States Geological Survey Volume 506

 
9781236185075: Bulletin - United States Geological Survey Volume 506

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1912 Excerpt: ...for quarry rock. East of Peoria Lake this gravel extends for 2 miles along the road and gives rise to a number of springs from the base of the bluffs. An approximate classification of the bowlders measuring 3 inches in diameter in the gravel under this bluff shows that about 50 per cent consist of dolomitic limestone, 10 of calcareous limestone, 10 of granite, 10 of quartzite, 6 of greenstone, 4 of yellow chert, 3 of diabase, 3 of local sandstone and shale, 2 of quartz, 1 of gneiss, and 1 of a rock resembling the conglomerate of Port Huron. Laminated silt and sand, which underlie the bowlder clay in the south bluff of Farm Creek below the mouth of Glendale Hollow, are probably also to be referred to the Illinoian. All of this drift was no doubt laid down in water coming from the Illinoian ice sheet, either directly in front of it or in channels under the ice. In either event it indicates a lowland where accumulations of unconsolidated materials remained almost undisturbed under an overriding sheet of ice. INTERGLACIAL EPOCH. The valleys in the area of the Illinoian till are more open than in the region of the later drift, and their ramifications have made farther inroads on the upland. This is especially apparent in the country southeast of Pekin and in Hollis Township, west of the river. This drift sheet has suffered superficial leaching and oxidation, and in few places contains any calcareous matter in its uppermost 3 or 4 feet. In some places there is a rusty ferruginous tinge near the surface of the till under the loess, as was noted in several exposures in the Lick Creek basin. In some of the ravines in the west part of sec. 32, Groveland Township, a reddish clay overlies the till. This is also leached. It is tough and contains a few pebbles, resemblin...

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