THE AGENCY OF ICE. 163 



regions the rocky foundation of which is such as to afford a 

 suitable soil. The agency of ice has been sucli as to bring to- 

 gether from remote countries the loose materials from the lime- 

 stone rocks, the slaty rocks, the marl beds, the granite rocks, 

 and the wearing of those materials into paste has transformed 

 them into that coating which really constitutes the bulk of our 

 agricultural soil. Those materials have been remodelled since 

 by atmospheric agencies ; they have been rained upon since the 

 time they were deposited, and of course the action of water has 

 carried far off to other places what had been first worked upon 

 by ice. But this is not very extensive and does not constitute 

 a part of the primary formation of agricultural soil. 



It would lead very far to enter into an extended discussion of 

 the manner in whicli ice can have produced these results. It 

 would probably excite a smile if I were to begin by saying that 

 the whole extent of the United States has at one time been cov- 

 ered with a sheet of ice many thousand feet in thickness ; and 

 yet geology can show that it was so. It would probably excite 

 doubt if it were stated that the whole sheet, moving from the north 

 in a southerly direction, has ground the loose materials resting 

 upon the surface of the earth to that paste which constitutes the 

 agricultural basis ; and yet it is so. It has been by a succession 

 of observations, starting from small beginnings, that this result 

 has been reached and is now recognized as a fact among geol- 

 ogists ; and in order to give you some idea of the process, I will 

 state what I know of operations of this kind which are still 

 going on at the present day. 



It is not my purpose to explain to you the physical laws regu- 

 lating the formation of glaciers. It is not my purpose to show 

 what are the causes which set those masses of ice in motion in 

 those regions where there are glaciers still in existence, for that 

 would occupy more time than I have before me. I want only 

 to speak of ice as a geological agency, and to show you what 

 connection exists between the former extension of ice fields over 

 the northern continents and the preparation of the earth for the 

 purposes of man. Masses of ice have existed which once cov- 

 ered our continent to a latitude the southerly limit of which 

 we hardly know precisely, and which have equally covered the 

 southern hemisphere to a latitude northwards which is also not 

 yet determined ; but I say these masses of ice have existed, and 



