738 



GEOLOGY 



deans (Fig. 500), conifers, ferns, and horsetails were the dominant 

 forms. In most of Europe, this group held possession of the land 

 throughout the period, though angiosperms appeared in Portugal 



^rw*^ 



Fig. 500. A cycadian trunk from the Black Hills, Dakota, Cycadeoidea 

 dakotensis Ward, Lower Cretaceous. (Ward.) 



before its close. Descendants of Jurassic types of plants also con- 

 tinued throughout the period in northwestern America. 



The introduction of angiosperms. The eastern and central 

 America angiosperms, including both monocotyledons and dicoty- 

 ledons, appeared early in the period, and developed so rapidly 

 that by the beginning of the next period they seem to have overrun 

 the continent. This is one of the most radical evolutions in the 



