File:Biennial report for 1913 and 1914; administrative report and economic and geological papers (1917) (14782998715).jpg

Identifier: biennialreportfo30illi (find matches)
Title: Biennial report for 1913 and 1914; administrative report and economic and geological papers
Year: 1917 (1910s)
Authors: Illinois State Geological Survey
Subjects: Geology
Publisher: Urbana
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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per surface of the drift, and thus of the lowersurface of the loess, wras obtained at a large number of places to determinewhether the surface of the drift sheet was a nearly level plain, or whetherit had considerable relief, at the time the loess mantle was spread upon it.Possible sources of the low-lying loess were then considered. RELATIONS OF LOESS AND DRIFTPre-loessial Surface The altitudes of the top or highest level at which the drift was foundat different points are shown on the accompanying map (PI. III). Theywere mostly obtained from leveling up from the outcrop of the loess-driftcontact to bench marks, or other points the elevations of which could be (109) 110 BIENNIAL REPORT FOR 1913 AND 1914 definitely determined from the topographic map. A few were obtainedfrom aneroid readings, the aneroid being checked with nearby bench marks.A few others were obtained from the records of water wells in which thedepth to the top of the drift was definitely known. In general the figures
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Fig. 8.—Bluff of loess along Mississippi River in Calhoun County, Illinois. indicate the highest elevation at which the drift was found in those places.In order that no exposure should be considered in which the loess was ofdoubtful character, no outcrops were included in this study in which the LOESS IN CANTON QUADRANGLE 111 thickness of the fine-grained pebbleless material above the drift did notexceed two feet. It may be seen from the figures on the map (PL III) showing theelevation above sea level of the top of the drift beneath the loess in differentplaces in the quadrangle, that the pre-loessial relief of the area was morethan 150 feet. The general slope of the top of the drift, beneath the loess,in this region corresponds quite closely to the present slope of the surface.The main divide of the region in pre-loessial time, as at present, extendedeastward from near the middle of the west side of the quadrangle, past thetown of Fairview, and thence a little north of east between

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