1876.] 63 [Hitchcock. 



I carefully examined, consists of piles of boulders, mostly rounded, 

 tossed about in rude heaps, the chinks between them being pretty 

 well filled with unstratified sand. The arrangement of the ridges of 

 boulders, with their convexities always to the south, or away from the 

 source of supply, together with the characteristic conical depressions, 

 left me in no doubt as to the origin of the island. 



"Martha's Vineyard, although cumbered with terminal rubbish, is 

 based upon the inclined tertiary clays which crop out from Gay Head 

 all along the north shore of the island. A considerable part of the 

 area is covered with glacial material; but from the cursory view ob- 

 tained by sailing along its shores and landing only once, I saw 

 nothing like the true arrangement of moraine ridges. It seemed a 

 confused mass of glacial rubbish, as if the ice had not rested long 

 enough in one place to mark its termination by a true morainal wall. 



" So far as I have studied extinct glaciers, wherever the terminal 

 and lateral material have been pushed along to any great distance, 

 the blocks are all more or less rounded. It is only the glacial tables 

 or blocks which are transported upon the surface of the ice that re- 

 tain their angular form." 



Lenticular Hills of Glacial Drift. By C. H. Hitchcock. 



The glacial drift, or till, composed of earth and glaciated or angular 

 boulders of various sizes, frequently up to ten feet in diameter, in- 

 discriminately mixed, without any of the assorting or stratifying ac- 

 tion of water, is very unequally distributed over southern and eastern 

 New Hampshire and eastern Massachusetts. Over large areas 

 scarcely any considerable accumulations of this till are found, and 

 ledges lie everywhere at or near the surface. Elsewhere the till 

 occurs in large amount, covering the ledges, which are scarcely ex- 

 posed over some whole townships near the coast. This till may be 

 of irregular thickness and distribution ; but generally, where it is 

 found plentifully, it is to a large extent massed in peculiar, oblong or 

 nearly round hills, which usually have quite steep sides and gently 

 sloping, rounded tops, the whole presenting a very smooth and regu- 

 lar contour. Their outlines as protracted upon a map are lenticular 

 in shape, whence their name. 



These hills are of all sizes up to one third or one half mile long, 

 with two thirds as great width, or they are sometimes nearly round. 

 In a few cases they are prolonged considerably beyond their usual 



