356 OKIGIN OF LIFE IN AMERICA 



interchange would have continued only between Europe and 

 South America. If the land bridge had then become discon- 

 nected with South America, and joined to western North 

 America, while the Antilles were submerged, the latest Euro- 

 pean emigrants would have taken refuge in California as the 

 last remnants of the old land sank into the Pacific. That 

 something of this kind actually took place I feel convinced, 

 although the details of these events must be founded largely 

 on geological studies which unfortunately are as yet insuffi- 

 ciently known. My own knowledge, moreover, of the geo- 

 logical features of the regions alluded to is only fragmentary. 

 Nevertheless, the little I have been able to gather does not 

 tend to contradict the general scheme of the theories I now 

 suggest. 



In later Cretaceous times a broad sea, as I have pointed 

 out on several occasions, separated western from eastern North 

 America, while the Pacific Ocean flooded a large portion 

 of the western States, so as to leave only a comparatively 

 narrow strip of land between the two seas. The Cretaceous 

 deposits can be traced all along the Pacific coast as far almost 

 as the extreme tip of Lower California. Here they suddenly 

 stop. The Cretaceous sea evidently did not cover the in- 

 teresting Cape Eegion of Lower California nor any part of 

 western Mexico. There are reasons for the belief that even 

 at this time the western part of the coast ranges of California 

 were not submerged, thus suggesting the existence of another 

 land-mass to the west of the Californian Sea. This land may 

 have been connected with the Cape Eegion of Lower Cali- 

 fornia, and thus with Mexico. By the end of Cretaceous time, 

 says Professor Smith,* the subsidence and erosion of the 

 western part of the continent had almost established a con- 

 nection between the Pacific Gulfs in California and Oregon 

 and the old Mediterranean Sea in the Mississippi valley. The 

 intervening isthmus was covered by extensive marshes. Pro- 

 fessor Smith tells us that the geographical conditions re- 

 mained the same in Eocene times as in the Upper Cretaceous, 

 except that the sea encroached still further on the land. Now 

 it is precisely at this time that we notice a striking affinity 



* Smith, J. Perrin, " Geological History of California," pp. 347348. 





