246 THE GEOLOGICAL HISTORY OF PLANTS. 



Charlotte Islands,* and still earlier in Virginia, f The 

 presumption is, therefore, that it came from the south. 

 It has, indeed, the facies of a southern hemisphere and 

 insular flora, and probably spread itself northward as far 

 as Greenland, at a time when our northern continents 

 were groups of islands, and when the ocean currents were 

 carrying warm water far toward the arctic regions. The 

 flora which succeeds this in the sections at Atau6 has no 

 special affinities with the southern hemisphere, and is of 

 a more temperate and continental character. J It is not 

 necessarily Upper Cretaceous, since it is similar to that 

 of the Dakota group farther south, and this is at least 

 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 coolness and continental character of 

 climate. It must, therefore, have been connected with 

 that elevation of the land which took place at the begin- 

 ning of the Cretaceous. During this elevation it spread 

 over all western America at one time or another, and, as 

 the land again subsided under the sea of the Niobrara 

 chalk, it assumed an aspect more suited to a warm cli- 

 mate, but still held its place on such islands as remained 

 above water along the Pacific coast and in the north, and 

 it continued to exist on these islands till the colder seas 



* " Reports of the Geological Survey of Canada." 



•|- Fontaine has well described the Mesozoic flora of Virginia, "Ameri- 

 can Journal of Science," January, 1879, and " Report on Early Mesozoic 

 Floras." 



^ In the " Proceedings of the Royal Society of Tasmania," 1S81, Mr. 

 R. M. Johnston, F. L. S., states that in the Miocene beds of Tasmania trees 

 of European genera abound. The Mesozoic flora of that island is of the 

 usual conifero-cyoadean type. Ettingshausen makes a similar statement 

 in the " Geological Magazine " respecting the Tertiary flora of Australia 

 and New Zealand, stating that, like the Tertiary floras of Europe, they 

 have a mixed character, being partly of types now belonging to the north- 

 ern hemisphere. 



