THE PLEISTOCENE OR GLACIAL PERIOD 853 



Either of the two great types of drift, the stratified and the un- 

 stratified, may overlie the other, or the two may be interbedded. 

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

 essential contemporaneity of origin. No agents but glacial ice and 

 glacio-flu.vial waters could have brought about such relations be- 



Fig. 565. A section of unst ratified drift till or bowlder clay, on bed- 

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



tween the stratified and unstratified drift over such extensive 

 areas. 



4. Distribution. 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) Within the area of its occurrence, the drift is measurably in- 

 dependent of topography. That is, its vertical range is as great 

 as the relief of the surface itself. Within the state of New York, 

 for example, it ranges from sea-level to the tops of the Adirondacks, 

 nearly 5,000 feet above. It is found in valleys and on hills, and 



