410 THE CANADIAN NATURALIST. [Vol. viii. 



stances, it seems highly probable that nearly the whole of North 

 America must have been submerged during the deposition of the 

 later portion of the Cretaceous series. It has been supposed, 

 indeed, that towards the close of the Mesozoic period the Rocky 

 Mountains formed a land barrier between two oceans, each of which 

 was tenanted by a distinct local fauna, but this hypothesis is not 

 borne out by the facts of the case as we now know them, and the 

 existence of Cretaceous rocks at very high elevations both in the 

 Cascade range and in the Rocky Mountains, goes far to prove 

 that some of the loftiest peaks of these two mountain chains owe 

 their elevation to movements of Post Cretaceous date. 



Trigonia Dawsoni and Astarte ventricosa, fron the Iltasyouco 

 River, are also found in the Jurassic rocks of the western slope 

 of the mountains in Nevada; and it may be that there is no 

 physical or geological break between the coast range of British 

 Columbia and the Sierra Nevada. Mr. Gabb has pointed out 

 that the Jurassic fossils of Nevada are probably of the age of the 

 Lias, and some of the Iltasyouco lamellibranchs, as has already 

 been stated, are barely distinguishable from European Liassic 

 species. On the other hand, the few Ammonites collected by 

 Mr. Dawson, so far as very fragmentary specimens enable one to 

 judge, appear to be conspecific for the most part with well known 

 forms from the English Inferior Oolite, though one, which has 

 been doubtfully referred to Perisphinctes anceps, may indicate 

 an horizon as high as the Oxford Clay or Coral R<'g. On the 

 whole, however, the evidence, as far as it goes, is in favour of the 

 supposition that these fossils from British Columbia belong to 

 the lower rather than to the upper part of the Jurassic series. 



