CHAPTER V 



CLASSIFICATION AND GENESIS. 



Althougli we need not now study the causes of such astonishing vari- 

 ations in climate as have taken place in post-Tertiary time, we must assume 

 an ice-sheet covering all New England except perhaps a few of the highest 

 peaks. For the present we must investigate the order of events. The 

 l^igher questions invoh'ing the causes of geological climates must come 

 later. As it is the first office of science to classify facts and discover their 

 underlying principles, it remains for us to make a detailed examination of 

 the known facts and, if possible, to reach a satisfactory classification and 

 explanation of them. The moment we enter upon this inquiry, however, 

 we confront the difiiculty of isolating the glacial sediments from the other 

 glacial deposits or from other forms of water transportation, and our subject 

 at once broadens so as to include every form of superficial deposit. 



Probably northern Grreenland typifies more nearly than any other 

 known country the condition of New England at the time it was covered 

 by ice. It is known that the interior of that country is covered by a great 

 continuous snow field that rises above all. the hills and most of the moun- 

 tains and is discharged into the sea by broad glaciers. During the greater 

 part of the Ice age the glaciers of New England were practically confluent. 

 The ice then extended far out into the present Gulf of Maine, and was there 

 discharged into the ocean as icebergs or as melting waters. The drift 

 which was at that time deposited near the ice front is now beneath the 

 Atlantic. But the last part of the Glacial period saw the extremity of the 

 retreating ice confronted by the sea along a very crooked line situated over 

 what is now the dry land. The sea then stood at about 230 feet above its 

 present level, and broad arms of salt water extended far into the interior of 

 the State along the principal valleys. Our problem involves both the study 



