194 THE GEOLOGICAL HISTORY OF PLANTS. 



of the United States and the corresponding formations 

 in Canada. On the eastern side of the American conti- 

 nent, in Virginia, the Potomac series is supposed to be 



of Lower Cretaceous age, 

 and here Fontaine, as 

 already stated, has found 

 an abundant flora of cy- 

 cads, conifers, and ferns, 

 with a few angiosperm- 

 ous leaves, which have 

 not yet been described. 



In the Canadian Eocky 

 Mountains, a few hun- 

 dreds of feet above the 

 beds holding the before- 

 mentioned species, are the 

 shales of the Mill Creek 

 known in the Cretaceous of Canada, series, rich in many spe- 

 cies of dicotyledonous 

 leaves, and corresponding in age with the Dakota group, 

 whose fossils have been so well described, first by Heer 

 and Capellini, and afterward by Lesquereux. We may 

 take this Dakota group and the quader-sand stone of Ger- 

 many as types of the plant-bearing Cenomanian, and may 

 notice the forms occurring in them. 



In the first place, we recognise here the successors of 

 our old friends, the ferns and the pines, the latter repre- 

 sented by such genera as Taxites, Sequoia, Glyptostrobus, 

 Gingko, and even Pinus itself. We also have a few 

 cycads, but not so dominant as in the previous ages. 

 The fan-palms are well represented, both in America and 

 in the corresponding series in Europe, especially by the 

 genus Sahal, which is the characteristic American type of 

 fan-palm, and there is one genus which Saporta regards 

 as intermediate between the fan-palms and the pinnately 

 leaved species. There are also many fragments of stems 



Fig. 69. — Stercalia and Laurophyllum 



