106 BOARD OF AGRICULTURE. 



any of the Northern States, have been covered with salt water 

 since their npheaval, or certainly not since the post-tertiary 

 period. We find no marine shells, or ancient beaches, no 

 evidence of the existence of cretaceous deposits, in any of the 

 northern sections of our country. If seas had prevailed here, 

 these evidences of the fact would most certainly appear. 

 AVhat is known as the glacial theory, much more satisfactorily 

 clears up the mystery, and sheds light upon the interesting 

 problem. It is supposed that in a remote epoch of the earth's 

 history, the whole northern section of our country was covered 

 with a vast sheet of ice ; that this icy covering moved down 

 from the north in accordance with the laws governing the 

 movements of glaciers, and brought along with it the vast 

 accumulations of bowlders and drift material which we find 

 everywhere deposited. 



If this be true, curiosity may lead you to inquire how far 

 these materials have been transported, and how long the ice 

 continued. The first question can be answered approximately, 

 the second rests upon hypothesis. Observed facts show that 

 some of these materials have been transported ten, twenty, 

 fifty, and in some cases, one hundred and fifty miles. I have 

 before alluded to this point, and will not dwell upon it longer. 

 It is supposed the ice-covering continued through a period of 

 at least one hundred thousand years, and that it commenced 

 about two hundred thousand years ago. This is, however, 

 pure speculation. Now, this sheet of ice must have been of 

 immense thickness, for it has left evidence upon the sides of 

 our mountains of this fact. 



Prof. Dana savs that it could not have been less than 

 five thousand feet in thickness in the more northern portions 

 of New England ; and in the southern portions, it was prob- 

 ably two thousand feet. There are certain facts which lead 

 us to believe that this view is correct, for the ice must have 

 covered very nearly the whole of the mountain regions of New 

 Hampshire. Only about one thousand feet of Mount Wash- 

 ington was left uncovered ; and the whole of Monadnock, and 

 the Green Mountains of Vermont, were hidden by the ice. 

 The same may be said of the mountains in the western part 

 of Massachusetts, and those in the Adirondack region. 



Whenever, gentlemen, you visit Monadnock, a mountain 



