214 THE GENESIS AND MIGRATIONS OF PLANTS 



ments of the American land in Cretaceous and early Eocene 

 times, included the existence of a great inland sea of warm 

 water extending at some periods as far north as the latitude of 

 55°, and that this must have tended to much equality of cHma- 

 tical conditions. 



We* cannot certainly affirm anything respecting the origin 

 and migrations of these floras, but there are some probabiHties 

 which deserve attention. The ferns and cycads of the so- 

 called Lower Cretaceous of Greenland are nothing but a 

 continuation of the previous Jurassic flora. Now this was 

 established at an equally early date in the Queen Charlotte 

 Islands,^ and still earlier in Virginia.^ The presumption is, 

 therefore, that it came from the south. It has indeed the 

 facies of a southern hemisphere and insular flora, and pro- 

 bably spread itself northward as far as Greenland at a time 

 when the American land was long, narrow, and warm, and 

 when the ocean currents were carrying tepid water far tovv^ard 

 the arctic regions. The flora which succeeds this in the sec- 

 tions at Atane and Patoot has no special affinities with the 

 southern hemisphere, and is of a warm temperate and conti- 

 nental character. It is very similar in its general aspect to 

 that of the Dakota group farther to the south, and this is 

 probably Middle Cretaceous. This flora must have originated 

 either somewhere in temperate America, or within the arctic 

 circle, and it must have replaced the older one by virtue of 

 increasing subsidence and gradual change of climate. It must 

 therefore have been connected with the depression of the land 

 which took place in the course of the Cretaceous. During this 

 movement it spread over all Western America, and as the land 

 again arose from the sea of the Niobrara chalk, it assumed an 

 aspect more suited to a cool climate, or moved southward, 



^ Reports Geological Survey of Canada. 



2 Fontaine has well described the Mesozoic flora of Virginia, American 

 Journal of Science^ January, 1879. 



