ANCIENT GLACIERS. 67 



for the most part, foreign to the localities, and can be 

 traced to outcrops of rock at the north. The boulders 

 scattered over the surface of Long Island, for example, 

 consist largely of granite, gneiss, hornblende, mica slate, 

 and red sandstone, which are easily recognised as frag- 

 ments from well-known quarries in Connecticut, Ehode 

 Island, and Massachusetts; yet they have been transported 

 bodily across Long Island Sound, and deposited in a het- 

 erogeneous mass through the entire length of the island. 

 Not only do they lie upon the surface, but, in digging into 

 the lines of hills which constitute the backbone of Long 

 Island, these transported boulders are found often to make 

 up a large part of the accumulation. Almost any of the 

 railroad excavations in the city of Brooklyn present an 

 interesting object-lesson respecting the composition of a 

 terminal moraine. 



All these things are true also of the lines of moraine 

 farther east, as just described. Professor Shaler has traced 

 to its source a belt of boulders occurring extensively over 

 southern Rhode Island, and found that they have spread 

 out pretty evenly over a triangular area to the southward, 

 in accordance with the natural course to be pursued by an 

 ice-movement. Nearly all of Plymouth County, in south- 

 eastern Massachusetts, is composed of foreign material, 

 much of which can be traced to the hills and mountains 

 to the north. Even Plymouth Rock is a boulder from the 

 direction of Boston, and the " rock-bound " shores upon 

 which the Pilgrims are poetically conceived to have land- 

 ed are known, in scientific prose, as piles of glacial rub- 

 bish dumped into the edge of the sea by the great conti- 

 nental ice-sheet. 



The whole area of southeastern Massachusetts is dot- 

 ted with conical knolls of sand, gravel, and boulders, sepa- 

 rated by circular masses of peat or ponds of water, whose 

 origin and arrangement can be accounted for only by the 

 peculiar agency of a decaying ice-front. Indeed, this 



