Among the difficulties which beset the student of Pleistocene deposits in the field, none cause greater perplexity than the real or apparent intermingling of strata or masses belonging to different portions of this period. I t thus sometimes appears as if masses of different drifts are transposed or interglacial formations are out of place.
During the past year two striking illustrations of such mingling were observed by the writer, the one at Des Moines, Iowa, showing a transposition of yellow and gray loesses and a mixing of fossiliferous gray loess with Wisconsin drift, and the other at Sioux Falls, South Dakota, showing fossiliferous silt apparently between two drifts.
Location.—This . . .