STUDIES FOR STUDENTS. 529 



II. Formations produced by the combined action of Pleistocene 

 glaciers and glacial drainage (assorted drift). — The iarge amount 

 of water derived from the melting of the ice, and the added 

 amount contributed by rains, constituted a very important aux- 

 iliary agency and gave rise to much assortment and re-arrange- 

 ment of the drift. 1 



Three classes of deposits may be discriminated, those that 

 are the products 1) of subglacial streams, 2) of superglacial 

 streams, and 3) of marginal waters. 



1. Deposits of subglacial streams. 



Subglacial waters may be classified in two groups, the first 

 embracing those which flowed in well established tracts or tun- 

 nels formed in the base of the ice, the second embracing those 

 which flowed in a more diffuse and irregular way under the ice. 

 These appear to have given rise to corresponding deposits. 



(1) Osars (asar) or eskers (frames of many authors). — It is 

 thought to be now beyond question that trains of gravel accumu- 

 lated in tunnels formed by subglacial streams and that these, 

 on the disappearance of the ice, formed ridges. The course of 

 these seems to have been conditioned partly by the slope of the 

 land and partly by the direction of glacial movement. They are 

 best developed where these approximately coincide. It can 

 scarcely be said, however, that osars are limited to such coinci- 

 dence. The more extensive, branching and typical forms were 

 probably also conditioned by stagnant or approximately stagnant 

 states of the ice in its vanishing stages. The Scandinavian term 

 asar seems entitled to precedence both because these remarkable 

 forms are typically developed there, and because they first 

 received notable attention there. The term eskers is coming to 

 be used somewhat freely by many American writers as a synonym 

 and is preferred by some for phonic reasons, while the term kames 

 is being used for a cognate variety of gravel accumulations, to 



1 It is to be noted that only that assortment of the drift which was contemporaneous 

 with the ice epoch and connected with the ice action is here taken into consideration. 

 Modifications of the drift that took place subsequent to the disappearance of the ice, 

 or independent of it, belong to a class quite distinct from that under discussion here. 



