Cenozoic Floras Around the Northern Pacific 79 



and lowered temperature quite as definite as the advance of ice 

 sheets from the north. The subsequent withdrawal of these 

 species northward to and beyond the Monterey Peninsula is an 

 equally definite record of a return to southern California of the 

 dry and warm climate which now characterizes it. The relation 

 of the Pleistocene floras of California to the modern coastal 

 closed-cone pine forest, with its present differentiation into floris- 

 tic units, has been so fully discussed by Mason"" that it need only 

 be mentioned here. 



Pleistocene floras in Oregon, Washington, and British Colum- 

 bia have not been extensively collected and studied, but those 

 now available indicate the probable existence of differences from 

 those of California which were consistent with the differences 

 in latitude. A small flora from near Fairbanks, Alaska,^ is made 

 up of Betula, Salix, and other boreal types. It may be suggested 

 that in the Pleistocene there was essentially as great diversity in 

 the forests from south to north along the Pacific Coast as now. 



The Pleistocene floras of Asia have only recendy become an 

 object of study, especially in connection with the occurrence of 

 early man in China."' *^ On the basis of our present incomplete 

 knowledge, it may be supposed that they differed only in a small 

 degree from the modern forests of the regions where they have 

 been collected. 



In discussing the history of the Cenozoic plants bordering the 

 northern basin of the Pacific, particularly with reference to their 

 stratigraphic sequence and geographic distribution, it has been 

 necessary at various points in this paper to describe and interpret 

 the physical conditions under which they lived. This has been 

 essential because their distribution both in time and in space has 

 been conditioned by physical changes which have resulted in 

 their migrations. The major movements have been southward 



