26 AMERICAN JOURNAL 



that of the White Sea or the numerous gulfs in Siberia. This 

 gulf extended perhaps, in course of time, by action of the sea, 

 immersion of the land, and sinking of the boggy strata, to its 

 present extent. The separation of England and France, and 

 the submersion of large tracts of land between Ireland and 

 Portugal, seems even to have taken place in the time of man. 



The effect of this change* of the relations between land and 

 sea was that the isotherms, which in Siberia run nearly parallel 

 to the lines of latitude, were bent far up to the north. The 

 beech tree, which cannot withstand the severe winters of the 

 continental clime, extended from the mountains of middle Eu- 

 rope as far north as to Norway. Many arctic animals, as the 

 reindeer, were perhaps destroyed by this change of climate. 

 Many of the lower arctic animals have perhaps perished since, — 

 i. e., Hyalina alliarta, H. hammonis, Succinea groenlandica, 

 Vitrina beryllina, etc. 



It is now a question whether the arctic fauna on both sides of 

 the Behring Strait show a notable difference between the species ; 

 and can it be deduced from the present fauna of Greenland and 

 Arctic America that these countries have been in closer con- 

 nection with the old world than with America ? 



The mammalia of the circumpolar fauna are considered spe- 

 cifically distinct by most authors ; even the reindeer is, accord- 

 ing to Agassiz, distinct. The only mammal of Iceland which 

 does not appear to have been introduced by man or the ice, Mus 

 islandicus, Tieneman, belongs to a genus not found in America."}" 

 It is still a question if the mollusca are specifically identical on 

 both sides of the Behring:. The most of the land mollusca of 

 temperate North America are generically different from those of 

 Europe. Helicogena, Clausilia, are thus not found in America. 

 Arionta, Gampylicea, Pomatia, are found on the north-west coast 

 of America, but not at all in the Eastern States. Some genera, 

 very numerous in species on the American side, are represented 

 in Europe by few, but very distinct species, as Triodopsis (per- 

 sonata), Discus. In the tropical parts of America the discre- 

 pancy of the fauna with that of the old world is still greater. 

 Thus Auchenia and Rhea represent, in America, Struthio and 

 Camelus of the old world. Mullcria corresponds to Atliceria, 



* Besides this general rise of land, and subsequent immersion, there 

 seem to have been several more local changes of land and sea, repeated 

 periodically in the Baltic. The White Sea has been in connection with 

 the Baltic through Finland, having left several arctic animals not to be 

 found in the Kattegat or the Belts, thus forming a secondary glacial pe- 

 riod for those countries. 



f Steenstrup. 



