CRITERIA OF GLACIATION 619 



ranges from sea-level to the tops of the Adirondacks, nearly 5,000 

 hit above. It is found on hills and in valleys, and on plains, 

 plateaus, and mountains, indiscriminately, though not usually in 

 equal amounts, (b) Locally the drift is so disposed as to make the 

 surface rougher than it would be otherwise, and in other places so 

 as to give it less relief (Figs. 512 and 513). (c) In constitution it is 

 im-usurubly independent of present drainage basins. Thus, mate- 



Fig. 509. A section of unstratified drift, till or bowlder clay, on bed-rock. 

 Newark, N. J. (N. J. Geol. Surv.) 



rials from one drainage basin are found in the drift of other drainage 

 basins so commonly as to make it clear that present divides did not 

 constitute divides to the ice. (d) Various sorts of material in the 

 drift at certain points are so related to their sources as to make it 

 clear that they were carried upwards, in some cases hundreds of 

 feet, above their original sites, (e) A considerable area in south- 

 western Wisconsin, and the adjacent parts of Illinois, Iowa, and 

 Minnesota, is without drift. This driftless area is neither notably 

 higher nor lower than its surroundings, and glacial ice seems to be 

 the only agent which could have spared it, while covering its sur- 



