74 THE ICE AGE IN CANADA. 



fluvatile denudation in Pliocene and pre-Pliocene times 

 has cut a trench to a depth of 800 feet below the present 

 water level of the St. Lawrence, and that the glacial 

 action of the Pleistocene has polished and grooved its sides 

 and probably its bottom, and piled up clehris at its mouth.* 

 I need hardly say, after the discussions on the subject, 

 that the reference of the cutting of lake basins and fiords 

 to glaciers in the ice age, against which I have argued 

 ever since 1866, has been altogether exploded. 



(1) This being admitted, and also the fact established, 

 by the most convincing evidence, of the great depression 

 of our continents in the glacial or Pleistocene age, it 

 follows that the first or oldest of the Pleistocene deposits, 

 the till or boulder-clay, was laid down during a time of 

 subsidence, in which the northern land was slowly sinking 

 under the sea. We leave untouched at present the mode 

 of deposition of boulder-clay and of polishing and stria- 

 tion of rock-surfaces under it, merely noting that the 

 boulder-clay proper is confined to the plains and valleys, 

 where it often contains marine remains. The hills show 

 evidence of glacier-movement down their valleys, and 

 of the formation of moraines, and sometimes of patches 

 of an indurated ground moraine or hard till, different 

 from ordinary boulder-clay. 



(2) The formation of the Leda clay and interglacial 

 deposits, and of the similar deposits on the western 

 plains, belongs to the time when this region had subsided 

 beneath the waters, with tracts and islands of higher 

 lands projecting. The differential character of this eleva- 

 tion, whereby certain parts of the then submerged areas 

 stood higher than others, will be mentioned later. 



* Notes on Pleistocene of Canada, 1872. 



