486 THE POPULAR SCIENCE MONTHLY 



After the Glacial epoch was past the climate became warmer, and 

 many mollusca crept slowly up the coast, from the warm waters of 

 Lower California. This southern type reached as far north as Santa 

 Barbara in the upper San Pedro epoch of the Quaternary, during which 

 time the sea probably had a temperature as warm as it now is on the 

 shores of Lower California. 



This warming up of the west coast was no mere local phenomenon, 

 for the same thing occurred at the same time on the eastern coast of 

 America, when a warm-water fauna ranged up to the Champlain dis- 

 trict. And also in Europe the climate after the Glacial epoch was, for 

 a little while, warmer than it is at present. After the San Pedro epoch 

 on the west coast, and the Champlain in the east the climatic conditions 

 became approximately what they now are, although it may well be that 

 the Terrace epoch had a larger rainfall than that of the present. 



Summary 



In the foregoing pages it will be noted that during all the known 

 Paleozoic the west coast enjoyed a warm and probably tropical climate, 

 with some suggestion of a northward march of the isotherms, reaching 

 a culmination in the Upper Carboniferous. There is then some indi- 

 cation of a southward recession of the isotherms in the Permian, and 

 a renewed northward advance in the Lower Triassic. This continued 

 until the middle of the Jurassic, but the farthest north was never again 

 reached in the Pacific waters. 



In the Upper Jurassic and the Lower Cretaceous another consid- 

 erable southward recession of the isotherms is indicated, followed by a 

 renewed northward advance in the middle of the Cretaceous. But this 

 advance did not reach so far north as that of the Middle Jurassic. The 

 Eocene epoch shows the temperature of the west coast nearly holding its 

 own, but with a probable slight reduction. The Miocene climate had 

 grown considerably cooler than that of the Eocene, and by the Pliocene 

 it was already rather cold as far south as California. The early Quater- 

 nary climate was probably even colder than the Pliocene, for there we 

 have the local ice-sheets in the high mountains of California. The post- 

 Glacial amelioration of climate is as distinct here as it was in eastern 

 America, and in Europe, and probably as short-lived. Middle and late 

 Quaternary time was probably much longer than we have been accus- 

 tomed to consider it, and there have doubtless been considerable fluctua- 

 tions in our climate in that period, but we have as yet been unable to 

 decipher these in the geologic record of the west coast. 



