374 THE GREAT ICE AGE 



times contains marine shells, or passes into marine clays in its 

 horizontal extension, and invariably in its embedded boulders 

 and its paste, shows an unoxidized condition, which could not 

 have existed if it had been a subaerial deposit. When the 

 Canadian till is excavated and exposed to the air, it assumes a 

 brown colour, owing to oxidation of its iron, and many of its 

 stones and boulders break up and disintegrate under the action 

 of air and frost. These are unequivocal signs of a subaqueous 

 deposit. Here and there we find associated with it, and es- 

 pecially near the bottom and at the top, indications of power- 

 ful water action, as if of land torrents acting at particular 

 elevations of the land, or heavy surf and ice action on coasts, 

 and the attempts to explain these by glacial streams have been 

 far from successful. A singular objection sometimes raised 

 against the subaqueous origin of the till is its general want of 

 marine remains ; but this is by no means universal, and it is 

 well known that coarse conglomerates of all ages are generally 

 destitute of fossils, except in their pebbles, and it is further to 

 be observed that the conditions of an ice-laden sea are not 

 those most favourable for the extension of marine life, and that 

 the period of time covered by the glacial age must have been 

 short, compared with that represented by some of the older 

 formations. 



It follows from all this that the great " continental moraine," 

 which the United States Geological Survey has now "delineated 

 for several thousand miles extending from the Atlantic to the 

 Pacific," cannot be a glacier moraine, but must be, like its 

 great continuation northward, the Missouri coteau, a margin 

 of sea drift, and that we must explain the whole of the drift 

 of the American continent by the supposition, first, of a period 

 of elevation of the hills and subsidence of the valleys in which 

 there were great accumulations of snow on the Western Cor- 

 dillera ; the Laurentian axis, and the Appalachians and Adiron- 

 dacks radiating in every direction from these points, while 



