484 TEE POPULAR SCIENCE MONTHLY 



as in the Upper Jurassic, the evidence is conflicting, for cycads are 

 known in both formations. 



In the Lower Cretaceous epoch there was a sharp contrast between 

 conditions on the Pacific and those on the Atlantic side of America. 

 In the Atlantic waters coral reefs extended as far north as Texas, while 

 no corals at all are known in the Pacific waters of America in Cali- 

 fornia. In the Upper Cretaceous, on the other hand, coral reefs ex- 

 tended to Ensenada, Lower California, lat. 31° 30' N"., while in the 

 Atlantic waters they did not reach so far north. In other words, the 

 Pacific waters on the western side of America became warmer in Upper 

 Cretaceous time than they were in the preceding epoch, while in the 

 Atlantic the conditions were reversed, as was the case also in southern 

 Europe, where coral reefs extended much further north in the Lower 

 Cretaceous than they did in the Upper Cretaceous. 



The change in faunal geography in western America about the 

 middle of the Cretaceous period is very remarkable. The Knoxville 

 epoch had a boreal fauna, while with the opening of the Horsetown 

 epoch the facies changed rather abruptly, and an Indian fauna came 

 in. Swarms of ammonites of Indian t}^pe occupied the shallow mar- 

 ginal sea, showing at least a great change in geographic connections, 

 if not in climate. It has been suggested by the writer that the opening 

 of the Bering Sea passage during the Mariposa epoch of the Upper 

 Jurassic and the Knoxville epoch of the Lower Cretaceous would ac- 

 count satisfactorily for the change of facies and the lowering of the 

 temperature at that time. The closing of this passage near the end of 

 the Knoxville epoch explains the change of facies from the boreal to 

 the Indian type of fauna, and also the accompanying rise of oceanic 

 temperature on the coasts of western America. 



The favorable conditions, inaugurated in the middle of the Creta- 

 ceous, continued throughout the Chico epoch, during which coral reefs 

 extended up to Ensenada, Lower California, N. lat. 31° 30', and a 

 warm climate prevailed even in Alaska. Beef-building corals extended 

 up to the middle of California, but they formed no reefs, since there 

 were no stretches of clear sheltered waters in which they could flourish. 



Neozoic Climates of the West Coast 



The Eocene climate of the west coast was nearly the same as that 

 of the Upper Cretaceous. The marine deposits have numerous mol- 

 luscan genera that are now confined to the tropics, and on the land 

 palms abounded in California, Washington and Alaska. No reef-build- 

 ing corals of this age are yet known anywhere on the west coast, and 

 it is probable that the marine temperature was slightly below that 

 necessary for their existence in this region. The climate of the coast, 

 from California to Alaska, was probably very much like that of the 



