W. J. McGee — Geology of the Mississippi Valley. 355 

 Classification of the Glacial Deposits of the Mississippi Vallet. 



Epochs. 



Members. 





EPOCH III. 



Member No. 1. 



A whitish-yellow, loess-like clay, unstrati- 

 fied, free from gravel, sand, and boulders. 



Member No. 2. 



Very pebbly and gravelly clay, with sand, 

 and small rounded and water-worn boulders. 



Member No. 3. 



Coarse yellowish clay, with sand, gravel, 

 pebbles, and large angular, subangular, and 

 rounded boulders, sometimes striated. It is 

 sometimes imperfectly stratified, and contains 

 lumps of blue clay. 



EPOCH II. 



Member No. 4. 



A blue clay, often fine and clean, but some- 

 times with sand, gravel, and boulders, many 

 striated. It frequently contains wood and 

 other organic substances. 



Member No. 5. 



Dirty-yellow or brownish clay or sand, 

 with much gravel, pebbles, and boulders both 

 rounded and flattened, and often striated. 



EPOCH I. 



Member No. 6. 



Deep-brown gravel or clay, with yellow 

 streaks; cemented into a ferruginous con- 

 glomerate where sandy and pebbly. 



to the general level, as is sometimes the case, this member may be 

 found only on the brows of the hills, having been removed from 

 their bases by erosion, and evidently never deposited on their 

 summits. 



Stratification has never been observed in this member, except 

 where it has been re-arranged by fluviatile agencies, and mixed -with 

 sand and gravel, as it frequently is in "bottoms." It has the "vertical 

 internal structure " described by Pumpelly, which characterizes the 

 loess of China, and vertical cracks and fissures form in it during 

 seasons of drought. In consequence it washes easily, especially in 

 a vertical direction, and surfaces covered by it are characterized by 

 great numbers of steep-sided and narrow, irregularly ramifying 

 ravines. In this respect, as in many others, it strikingly resembles 

 the loess of the Missouri Valley, — the " bluff-deposit " of several 

 American geologists. Indeed, it has been traced by the writer, with 

 no important breaks, from the Missouri, where characteristically 

 developed, into the most north-easterly portions of Iowa; and at 

 no place could any essential or well-defined distinction be drawn 

 between successive sections. True, the materials are not so finely 



