372 THE GREAT ICE AGE 



Mountains the bottom of the drift consists of gravel not 

 glaciated. This extends to about one hundred miles east of 

 the mountains, and must have been swept by water out of their 

 valleys. The boulder clay resting on this deposit is largely 

 made up of local debris^ in so far as its paste is concerned. It 

 contains many glaciated boulders and stones from the Lauren- 

 tian region to the east, and also smaller pebbles from the 

 Rocky Mountains, so that at the time of its formation there 

 must have been driftage of large stones for seven hundred 

 miles or more from the east, and of smaller stones from a less 

 distance on the west. The former kind of material extends to 

 the base of the mountains, and to a height of more than 4,000 

 feet. One boulder is mentioned as bemg 42 x 40 x 20 feet in 

 dimensions. The highest Laurentian boulders seen were at an 

 elevation of 4,660 feet on the base of the Rocky Mountains. 

 The boulder clay, when thick, can be seen to be rudely strati- 

 fied, and at one place includes beds of laminated clay with 

 compressed peat, similar to the forest beds described by 

 Worthen and Andrews in Illinois, and the so-called interglacial 

 beds described by Hinde on Lake Ontario. The leaf beds on 

 the Ottawa river, and the drift trunks found in the boulder 

 clay of Manitoba, belong to the same category, and indicate 

 in the midst of the Glacial period many forest oases far to 

 the north, having a temperate rather than an arctic flora. In 

 the valleys of the Rocky Mountains opening on these plains 

 there are evidences of large local glaciers now extinct, and 

 similar evidences exist on the Laurentian highlands on the east. 

 A recent paper of Dr. G. M. Dawson on the Palaeography of the 

 Rocky Mountains illustrates in a most convincing manner the 

 changes which have occurred in the Cordillera of North 

 America, and the differential elevation and depression which 

 have affected its climate in the later geological periods.^ 



Perhaps the most remarkable feature of the western drift region 

 ^ Transactions Royal Society of Canada, 1890. 



