60 ON THE LAND AND FRESH-WATER 



■water snails should have travelled the entire breadth of this great 

 continent, and have surmounted such obstacles as a mountain 

 chain, the highest peaks of which are from 15,000 to 18,000 feet 

 above the level of the sea, and clothed with perpetual ice and 

 snow, I leave for naturalists to determine. 



The large proportion of marine invertebrata common to 

 the coasts of eastern North America and northern Europe has 

 been thought to imply the existence of a pathway across the 

 Atlantic since the creation of the existing flora and fauna. We 

 have seen that eight at least (and probably double that number) of 

 the inland mollusca of Canada also inhabit northern Europe. Some 

 such theory as the one I have alluded to, would seem neces- 

 sary to explain this rather ■ peculiar geographical distribution. 

 Dr. Hooker's theory of the south westward migration of the 

 Scandinavian flora, and of its subsequent return under altered 

 physical circumstances, would seem to be doubtful on geological 

 grounds, also from the Darwinian reasoning called in to support 

 the latter half of his hypothesis. Dr. Dawson has cited the case 

 of two species of Solidago living on Mount Washington, one of 

 which (S. thyrsoidea,) has a limited range in northeastern America* 

 while the other (S. virgaurea,) has a widely extended distribution, 

 living as far north in Arctic America as from 55° to 65°, occur- 

 ring also in the Rocky Mountains, in Great Britain, Norway, and 

 many places in temperate Europe. He suggests that the plants 

 which extend over so large an area, may belong to the older Arc- 

 tic flora, and that the other species, of very local distribution, may 

 belong to a newer flora. (The two species cited are not perhaps 

 the best examples that might have been chosen to support this 

 view, as they have been considered identical by some botanists. 

 I would suggest the two cranberries, Vaccinium oxycoccus, and 

 V. maerocarpon, as unquestionably distinct species, illustrating the 

 same point.) If this theory be correct, it may be that those Lower 

 Canadian shells which have a wide geographical distribution may 

 be members of an older fauna than that which is more especially 

 characteristic of a limited area in northeastern America. Judging 

 from our present knowledge of the older post-pliocene deposits of 

 Canada, it is quite remarkable that the species found in the marine 

 beds are almost universally of very wide distribution. 



The science of arohaeo-geology, or in other words, the connection 

 between geology on the one hand and archaeology on the other, 

 may receive benefit from a much more rigorous comparison be- 



