THE GENESIS AND MIGRATIONS OF PLANTS 211 



the intervention of any other formation, ^ are beds rich in 

 plants of much more modern appearance, and referred by 

 Heer to the Miocene period, a reference which appeared at 

 the time to be warranted by comparison with the Tertiary 

 plants of Europe, but, as we shall see, not with those of 

 America. Still farther north this so-called Miocene assemblage 

 of plants appears in Spitzbergen and Grinnell Land ; but 

 there, owing to the predominance of trees allied to the spruces, 

 it has a decidedly more boreal character than in Greenland, as 

 might be anticipated from its nearer approach to the pole.^ 



If now we turn to the Cretaceous and Tertiary floras of 

 Western America, as described by Lesquereux, Newberry, and 

 Ward, we find in the lowest Cretaceous rocks known there 

 until very recently — those of the Dakota group, which may 

 be in the lower part of the Middle Cretaceous — a series of 

 plants 3 essentially similar to those of the Middle Cretaceous 

 of Greenland. To these I have been able to add, through the 

 researches of Mr. Richardson and Dr. G. M. Dawson, a still 

 earlier flora, that of the Kootanie and Queen Charlotte Island 

 formations, as old as the Gault and Wealden. It wants the 

 broad-leaved plants of the Dakota, and consists mainly of 

 pines, cycads, and ferns ; and only in its upper part contains 

 a few forerunners of the exogens.* These plants occur in beds 

 indicating shallow sea conditions as prevalent in the interior 

 of America, causing, no doubt, a warm chmate in the north. 

 Overlying this plant-bearing formation we have an oceanic 

 limestone (the Niobrara), corresponding in many respects to 



^ Nordenskiold, Expedition to Greenland, Geological Magazine, 1872. 



2 Yet even here the Bald Cypress ( Taxodium distichum), or a tree nearly 

 allied to it, is found, though this species is now limited to the Southern 

 States. Fielden and De ^2cixq.q, Journal of Geological Society, 1878. 



2 Lesquereux, Report on Cretaceous Flora. The reader not interested 

 in American details may pass over to the middle of page 213. 



* This flora has since been described in Virginia and Maryland by 

 Fontaine, and has been recognised in Montana by Newberry. 

 II 



