336 THE GEOLOGY OF THE LABRADOR COAST. 



were then widespread and most characteristic shells from 

 Greenland to Portland, Maine. The Leda especially, 

 abounding in every clay deposit, has now become wholly 

 extinct south of Spitzbergen and the 70th parallel of 

 latitude. 



An exceedingly small percentage, if any, of the species 

 has become wAo/fy ext\nct, the only instances occurring to 

 us being the Beluga vermontana, about which there must 

 be great doubt, since owing to the difficulty of distinguish- 

 ing the fossil species of whales, it may be the common 

 white whale and the new species of Fusus {F. labra- 

 dorensis), and, possibly, Bela robusta, described above. 

 ' A considerable number have become extinct in the 

 north temperate seas, owing to the great changes in the 

 climatic conditions. A parallel case is shown in the 

 southward migration and subsequent extinction in Eu- 

 rope of the musk-ox, polar bear, lemming, and other 

 quadrupeds now confined mostly within the limits of the 

 arctic circle. 



During the glacial period, or that of the deposition of 

 the glacial beds (Leda clay of Dawson), which are un- 

 mistakably rewashed terminal moraines left during the 

 incoming or coldest period of the Quaternary (when,, 

 we have every reason to believe, true glaciers of great 

 extent eroded the present river systems as far south as. 

 New York, the southern limits of the ice having been 

 indicated by Clarence King, Prof. G. F. Wright, and 

 others), there was a greater uniformity than now of the 

 climate ; but yet, as shown by the distribution of animal 

 life, there was a decided change from a purely arctic to 

 a sub-arctic climate, from Greenland southward. 



At present, the arctic or circumpolar fauna is restricted 



