CHAPTER XXXII 



THE QUATERNARY PERIOD — (OR PLEISTOCENE) 



In regions to which the great ice-sheets of the Glacial epoch 

 did not extend the transition from the Tertiary to the Quaternary 

 is perfectly gradual, so that it is often difficult or impossible to 

 determine to which division a given set of strata should be referred. 

 The seas at the end of the Pliocene had nearly the same extension 

 as at present, and on the same coasts the same deposits continued 

 to form. Even the Pliocene coral reefs continued uninterruptedly 

 into the Pleistocene, so that any separation at all seems arbitrary. 

 In the north, however, we find a very different state of things. 

 In immense regions of North America, Europe, and Asia occur 

 wide-spread evidences of vast glaciers and ice-sheets, in great 

 masses of drift which cover the plains and choke the valleys, in 

 successive lines of moraines, in great erratic blocks, sometimes 

 weighing thousands of tons, which have been carried long distances 

 from their parent ledges, and in the scored and polished rocks, 

 the rdches moutonnees and other features which we have learned 

 to be characteristic of ice action. The fossils also show the 

 prevalence of a cold climate in these latitudes, and thus all the 

 testimony agrees as to the great expansion of ice-sheets and gla- 

 ciers in the early Quaternary. 



The Glacial or Pleistocene Epoch 



At the end of the Pliocene, it is believed that the North Ameri- 

 can continent was at a higher level than now, especially to the north, 

 which favoured the accumulation of great masses of snow. It is 

 still a matter of debate whether there was a single Glacial age or 

 epoch, when the ice-sheet, once established, had many episodes of 



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