CHAPTER II. 



GLACIAL DRIFT. 



LLUSION has been already made to the former existence of an 

 immense thickness of ice over the whole of New Hampshire, as 

 well as the entire northern portion of our continent. This ice-sheet is 

 supposed to have been the natural accumulation of frozen moisture from 

 the atmosphere, requiring thousands of years* time for its gathering 

 together. Like the similar glacial masses upon both poles of the earth, 

 this one must have been slowly moving towards the equator, especially 

 near the melting edge. A formal proof of our statement is unnecessary, 

 since the phenomena presented to us universally over the state speak for 

 themselves ; and it will be difficult for any one to read an account of the 

 striation and embossment of the ledges, about to be described, without 

 believing in the existence of this sheet. As the subject is one of great 

 interest, and sound generalizations can be drawn only from observations 

 taken in every part of the state, much attention has been devoted to the 

 collection of facts during the whole time of our survey. Such of these 

 as are especially important will be named : hundreds of them will not 

 be mentioned. Many facts belong to a class, and we need therefore 

 describe with particularity only one example of them. Should the want 

 of time and space prevent a full discussion of the causes inducing the 

 cold climate, the method of transportation, the chronological date of the 

 period, and other related topics, the reader will find an excellent sum- 

 mary of conclusions of this nature in the preceding chapter. Treatises 

 VOL. III. 23 



