176 BOARD OF AGRICULTURE. 



polar region can have been less than ten or fifteen thousand 

 feet in thickness ; and this mass must have been pressed to- 

 wards the south, and have moved in a southerly direction. 



Whether that explanation be satisfactory or not, there is one 

 thing which is within the limit of observation — that over the 

 whole extent of the United States we find these polished sur- 

 faces exhibiting the same character as the surfaces which we 

 have under the glacier. Over the same extent of surface, we 

 have everywhere the loose materials which I have described, 

 with the peculiar character which distinguishes glacial action 

 from river action. To the same extent do we find angular 

 boulders resting upon surfaces which could not have been trans- 

 ported in the same manner as those which are around them, and 

 which, therefore, must have floated, as it were, over the rest of 

 the mass. 



Now, how could large boulders be floated in a current, and 

 the loose materials be at the bottom ? If it was an inundation, 

 if it was an " earthquake wave," as it is sometimes called, that 

 spread over the whole of this continent, and carried these loose 

 materials from the north, I ask why it is that the heaviest mate- 

 rials, the only ones which are angular, are always on the top of 

 the sheet of those loose materials, and that towards the bottom 

 you have the most minute ones? It is impossible to explain 

 that by the action of any current ; but the moment you assume 

 that a sheet of ice has been the working agency, you see at 

 once tliat below it you will have a grinding, crushing and 

 pounding, and above it the transportation of loose materials, 

 which undergo no friction ; and when the mass of ice melts 

 away you will have these heavy materials, which are angular, 

 resting on top of these more minute materials, which arc ground 

 and polislied. Therefore you explain the facts by the theory 

 which I advance, while no other theory has yet accounted for 

 it. And you account for another series of facts, which are 

 utterly unaccountable otherwise. After these immense sheets 

 of ice had been formed, they melted away, for they are no 

 longer there, and in melting away they produced large currents 

 of water. Just as now, at the lower end of glaciers, we have 

 everywhere streams issuing and flowing onward, so on the 

 southern edge of that sheet of ice there were streams forming, 

 and in proportion as the mass melted farther northwards the 



