2IO Evolution and Distribution of Fishes 



into the crests of the Mountains, and a parallel coast-range 

 was formed fronting the Pacific. Intense metamorphism of 

 the Cretaceous rocks is stated to have taken place. The 

 Rocky Mountains, with the elevated tableland from which 

 they rise, now permanently raised above the sea, were 

 gradually elevated to their present height. Vast lakes 

 filled depressions among them, in which, and on the plains 

 in front of the mountains, as in the Tertiary basins of the 

 Alps, and the Gondwana series of the Himalaya, enormous 

 masses of sediment accumulated. The slopes of the land 

 were clothed with an abundant vegetation, in which we may 

 trace the ancestors of many of the living trees of North 

 America. One of the most striking features in the later 

 phases of this history was the outpouring of great floods 

 of trachyte, basalt, and other lavas from many points and 

 fissures over a vast space of the Rocky Mountains and the 

 tracts lying to the West. In the Snake River region alone 

 the basalts have a depth of 700 to 1000 feet, over an area 

 of 300 miles in breadth." 



Such profound changes in the surface-crust of the earth 

 not only originated some of the loftiest mountain chains of 

 the world, they must also have served by cosmic stress and 

 strain to deepen the ocean areas, and give to these greater 

 fixity of position. During the process a gradual breaking up 

 and rearrangement of two great continental masses Arcto- 

 gaea and Notogaea evidently proceeded from this time 

 on to the Miocene period, when the present main outlines 

 of land and sea were effected. 



Second, With increased ridging up or elevation into 

 mountain chains — really high land-waves or crumplings 

 before denudation became conspicuous — of the land, the 

 waters of the earth would become increasingly restricted to 

 oceanic areas. So the extensive marshes, freshwater lakes, 

 and wide lagoon-rivers, would correspondingly become re- 

 duced in extent. These two conditions however would 

 be eminently favorable for, and would emphasize, pro- 

 gressive evolutionary changes in organisms. For they 

 would bring into sharp prominence the effects of isolation 

 of organisms; of new or changed environal states; of in- 

 creased littoral, sea, and ocean areas, in which originally 



