134 



THE ORIGIN AND EVOLUTION OF LIFE 



pre-Cambrian stock, giving rise to the phyllopods and other 

 true Crustacea of the Cambrian, and to the cirripedes or bar- 

 nacles of the Ordovician. 



Fig. 



America in Middle Devonian Times. 



Theoretic restoration of the North American continent (white), continental seas (gray), 

 and ocean (dark gray), in Middle Devonian (Hamilton) time. This period is 

 marked by the last extensive inundation of the Arctic seas, by the rise of the Schick- 

 chockian Mountains and many volcanoes in Acadia, and by the beginning of the 

 great Catskill delta built up by rivers from the rising Acadian region. Marine shark 

 and arthrodires become abundant, the American fauna of the Mississippi Sea shows 

 numerous brachiopods and bivalves, and the first evidence of a land flora with large 

 conifers (Dadoxylon) is found. Detail from a globe model in the American Museum 

 by Chester A. Reeds and George Robertson, after Schuchert. 



Reactions to Climatic and Other Environmental 

 Changes of Geologic Time 



Schuchert observes that there is no more significant period 

 in the history of the world than the Devonian^ (Fig. 32), for 

 at this time the increasing verdure of the land invited the 



^Pirsson, Louis V., and Schuchert, Charles, 1915, p. 714- 



