THE PLEISTOCENE OR GLACIAL PERIOD. 455 



Similar areas, though less extensive, occur in Kansas. 1 Dunes are 

 also conspicuous along many valleys in Kansas (see Fig. 2, PI. II, 

 Vol. I) and elsewhere. Small dunes are of common occurrence locally 

 in the humid region east of the Great Plains. Thus they abound 

 about the head of Lake Michigan and along its eastern shore, and 

 along some streams, especially those flowing through sandy tracts. 

 Even where dunes are wanting, wind-blown sand and dust are wide- 

 spread, though, excepting the loess, not generally in such quantity 

 as to be readily recognized. Much of this eolian sand is of very recent 

 deposition. 



Erosion, rather than deposition, was the great feature of the Quater- 

 nary in the interior, outside the region affected by the ice-sheets; and 

 in the erosive work, wind, running water, and ground-water have 

 cooperated. 



In the West. 



The Quaternary formations of the west belong to all the several 

 categories mentioned on p. 446, and to this list must be added the glacial 

 formations, not especially considered in the earlier part of this chapter. 

 But few of these various sorts of deposits have received close study 

 over any considerable area, though something is known of all. Among 

 the deposits which have been most closely studied are those of soaie 

 of the numerous lakes which existed at various points west of the 

 Rockies. Those of the Great Basin are best known (Fig. 536.) 



Lacustrine Deposits. Lake Bonneville. 2 — The most considerable 

 of the western Pleistocene lakes was Lake Bonneville, the body of 

 water of which Great Salt Lake is the diminutive descendant. Its 

 basin is believed to have been due to crustal deformation, and to have 

 antedated the lake itself by some considerable period. Previous to 

 the formation of the lake, the basin is thought to have been arid, a 

 conclusion based on the great alluvial cones and fans subsequently 

 covered by the lake. During the pre-lacustrine period of aridity, 

 such quantities of debris from the surrounding mountains were brought 

 into the basin as to bury the bases of the mountains to depths of per- 

 haps 2000 feet, at a maximum. 



1 See the Pratt, Syracuse, Lamed, and Kinsley sheets, U. S. Geol. Surv. 



2 Gilbert, Mono. I, U. S. Geol. Surv. 



