PKE-WISCONSIN DBIFT AND ASSOCIATED DEPOSITS. 75 



it decreases to 10 or 12 feet and over the greater part of the region is between 5 and 10 feet. 

 On slopes it is very thin, or wanting, because of erosion. 



It should be borne in mind that the loess here discussed is not the only deposit of its class 

 in the Pleistocene series. In not a few places, some of which are in southwestern Indiana 

 (see p. 67), loess occurs beneath or interbedded with the Illinoian drift. Loess is also found 

 to a limited extent on the outer part of the Wisconsin drift in central and eastern Illinois and 

 western Indiana. The loess just discussed is thicker as well as more continuous and widespread 

 than are similar deposits at other geologic horizons. 



PEORIAN OR POSTLOESSlAL SOIL AND WEATHERED ZONE. 



In Indiana there are but few places where the loess or its associated silts have been found 

 under the Wisconsin drift, and in these the weathered portion of the loess seems generally to 

 have been incorporated in the Wisconsin drift, leaving only the lower part for inspection. 

 Exposures near Greensburg were noted by Chamberlin 1 in his early explorations in that region, 

 and the writer found others in that vicinity. Concerning these exposures Chamberlin writes: 



At Greensburg and several points in the vicinity the interesting phenomena of the superposition of the newer 

 upon the older drift is well shown. The best exhibit is in the southeastern part of the city, where the superficial 

 deposits consist of about 7 feet of gray stony clay of fresh aspect, having suffered but a limited amount of superficial 

 oxidation, and containing pebbles with polished and scratched surfaces, unleached and unweathered. This stratum 

 is sharply terminated below and lies upon drift contrasted with it in high oxidation colors and the weathered char- 

 acter of the constituents. Examining more closely, the upper 2 or 3 feet of this lower stratum is found to be a loamy 

 clay, partially stratified, and containing numerous molluscan remains. This is manifestly the superficial deposit of 

 an old drift surface. 



The writer found what seems to be a good example of the preservation of the entire white 

 clay and its Peorian soil in an exposure in Coal Creek bluff in western Johnson County several 

 miles inside the Wisconsin border, as indicated by the following section: 



Section in bluff of Coal Creek near corners of sees. 29, 30, 31, and 32, T. 12, R. 3 E. 



Feet. 



Till (Wisconsin), yellow at top but shading into blue-gray at bottom 20 



Soil, black (Peorian) 1 



Silt or clay, pale, greenish yellow, pebbleless (post-Sangamon) 3 



Till (Illinoian), weathered and leached brown. Exposed o 



29 



The strongest evidence of an interval between the deposition of the loess and of the 

 Wisconsin drift is perhaps found in a comparison of the amounts by which the two have been 

 eroded. Although the erosion of the loess and associated silts is not strikingly greater than 

 that of the outer portion of the Wisconsin drift, the difference is perceptible and indicates an 

 interval greater than that between successive morainic systems of the Wisconsin drift. The 

 time, however, between the loess deposition and the culmination of the Wisconsin glaciation, 

 as marked by erosion and the forming of soil, seems to have been briefer than that between 

 the Illinoian glaciation and the loess deposition. 



SAND DEPOSITS ON THE LOESS. 



The sand deposits which appear on the surface of the loess in southern Indiana are found 

 mainly along the east sides of streams and have, apparently been carried to their present position 

 by wind. They commonly occur as short winding ridges scattered over a belt from 1 or 2 up to 

 several miles in width on the borders of the main valleys. They are very conspicuous east of 

 the Wabash Valley in northern and also in southern Vigo County and are a notable feature 

 south from there through Sullivan, Knox, Gibson, and Posey counties. Sand deposits are con- 

 spicuous along the east side of White River in Gibson and Pike counties but are more sparingly 

 distributed east of the south-flowing portion of the river in Daviess and Greene counties and 

 are rather scarce farther north. Notable deposits he east of the great bend of Eel River in 



1 Third Ann. "Rept. TJ. S. Geol. Survey, 1SS3, p; 333. 



