364 HISTORICAL GEOLOGY 



glaciation. Localization (of glaciation) is attributed to the two 

 great areas of permanent low pressure in proximity to which the 

 ice sheets developed." 1 



In conclusion we may say that, as is true of so many other 

 great natural phenomena, no one hypothesis or explanation is 

 sufficient to account for all the features of glacial epochs. Probably 

 several or all, or at least parts of several or all, of the above hypoth- 

 eses must be properly combined in order to explain the phenomena 

 of glaciation, and hence it is more readily understood why great 

 glacial epochs have not been more common throughout the history 

 of the earth. 



Post-Glacial (Recent) History of the Glaciated Area 



We have already shown that, about the beginning of the Glacial 

 epoch, the north Atlantic Coast region at least was much higher 

 than it is today, positive proof for this being afforded by the 

 submerged lower Hudson, St. Lawrence, and other channels 

 which must have been cut when the land was higher. Toward 

 the close of the Glacial epoch, and shortly after, we know that 

 the land was relatively lower even than it is today. It was 

 during this time of subsidence (sometimes called the Champlain 

 epoch) that the lower Hudson and St. Lawrence channels were 

 submerged and the sea coast was transferred to more nearly its 

 present position. But the land being even lower than now, the 

 lowlands of Long Island and in the vicinity of New York City 

 were under water and a narrow arm of the sea extended through 

 the Hudson and Champlain Valleys to join a broad arm of the 

 sea which reached up the St. Lawrence Valley and possibly even 

 into the Ontario Basin (see Fig. 220). This so-called Champlain 

 Sea existed at the time of the Nipissing stage of the Great Lakes 

 already described. Champlain Sea beaches, containing marine 

 shells and the bones of Walruses and Whales, have been found 

 at altitudes of about 400 feet near the southern end of Lake 

 Champlain, 500 feet at its northern end, and 600 or more feet 

 at the eastern end of Lake Ontario. In the lower Hudson Valley 

 the deposits of this age are about 70 feet above sea level, and 

 at Albany a little over 300 feet. The altitudes of these so-called 

 raised beaches show how much lower the land was during the time 

 i Chamberlin and Salisbury: College Geology, pp. 898-899. 



