Geology . s amantle overlying the drift (Fig. 525), and (2) between sheets of relations to the drift-sheets make it clear that it was accumu-lated at several different stages of the glacial period, but within theglaciated area the accumulation at one of these stages far exceeds 1 Von Richthofen, China. This author early (1877) advocated the eolian o-iginof the loess of China, but this explanation has not passed unchallenged. See tkertchleyand Kingsmill, Q. J. G. S., , 1895, pp. 238-254. 408 GEOLOGY. that ai all others, both in volume and areal extent. The loess deposited at thi
Geology . s amantle overlying the drift (Fig. 525), and (2) between sheets of relations to the drift-sheets make it clear that it was accumu-lated at several different stages of the glacial period, but within theglaciated area the accumulation at one of these stages far exceeds 1 Von Richthofen, China. This author early (1877) advocated the eolian o-iginof the loess of China, but this explanation has not passed unchallenged. See tkertchleyand Kingsmill, Q. J. G. S., , 1895, pp. 238-254. 408 GEOLOGY. that ai all others, both in volume and areal extent. The loess deposited at this Stage is often referred to as the loess, and is usually cor-related in time with the low an drift, though the strict accuracy of thiscorrelation has been questioned. It is at least later than the Kansan and Illinoian sheets of drift which it mantles, and earlier than theEarly Wisconsin which oveilics it. Locally, a thin mantle of loessoverlies the older part of the Early Wisconsin drift, and, more rarely. Fig. 525 —Loess overlying Kansan drift, with a thin band of pebbles at the junction; Iowa. (Calvin.) the younger. It even overlies the Late Wisconsin drift in places,though the Wisconsin drift-sheets are usually free from Loessdoes not appear in quantity between the Illinoian and Kansan for-mations, nor between the Kansan and sub-Aftonian. Outside the drift there are often two distinct sheets of loess. Theyare sometimes separated by a well developed soil zone, beneath whichthe surface of the lower loess shows the effects of prolonged weatheringand Uour. of Geol., Vol. IV, pp. 929-937. 2 Report on Crowleys Ridge, Ark. Geol. Sur., pp. 224-235. THE PLEISTOCENE OR GLACIAL PERIOD. 409 On portions of the Great Plains, and in some of the basins of theWestern mountain regions, there are deposits called loess, some ofwhich are closely similar to the loess of the drift region, while othersare quite different. But there is nowhere a development at all com-parable to
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