THE PLEISTOCENE OR GLACIAL PERIOD. 343 



deposition of the foliated drift beneath a body of ice. The strati- 

 fied drift shows by its structure that it was deposited by water. This 

 water doubtless sprang, very largely, from the melting of the ice. 



The structural relations of the two great types of drift will be referred 

 to again, but a conception of these relations is necessary to an under- 

 standing of the structure of the drift as a whole. Either type of the 

 drift may overlie the other, or the two may be interbedded; either 

 may grade laterally into the other, either may abut abruptly against 

 the other horizontally, or pockets of either may be enclosed in the 

 other. 



The association of the two is often such as to demonstrate their 

 essential contemporaneity of origin. Xo agents but glacial ice and 

 glacio-fluvial waters could have brought about such relations between 

 the stratified and unstratified drift over such extensive areas. 



(4) Distribution of drift. — The distribution of the drift is essentially 

 the same as that of the ice-sheets and glacial waters; but apart from 

 this general fact, there are several special features to be noted. 

 (a) The distribution of the drift is measurably independent of topog- 

 raphy within the area of its occurrence. Even in closely associated 

 localities, and outside the higher mountain areas, its vertical range 

 is as great as the relief of the surface itself. Within the limits of the 

 state of New York, for example, it ranges from sea-level to the tops 

 of the Adirondacks, nearly 5000 feet above. Within the area of its 

 occurrence it is generally found in valleys and on hills, and on plains, 

 plateaus, and mountains, indiscriminately, though not usually in 

 equal amounts. (b) The drift is sometimes so disposed as to make 

 the surface much rougher than it would be otherwise, and some- 

 times so as to give it less relief. This is illustrated by Figs. 478 

 and 479. (c) The drift is measurably independent of present drain- 

 age basins, so far as its constitution is concerned. Thus, materials 

 from one drainage basin are found in the drift of other drain- 

 age 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, sometimes hundreds of feet, 

 from their original sites, a point which is often readily established 

 in the case of large bowlders. Glaciers can do this sort of work, under 

 proper conditions, but water, unaided by ice, cannot, (e) A con- 



