2 BERRY— A POSSIBLE EXPLANATION 



restriction, as shown by the recurrent periods of glaciation, beginning 

 in pre-Cambrian time, of which that of the lower Permian was more 

 extensive than that of the famiHar Pleistocene. 



Climatic zones may also have been marked during the times of 

 land emergence, when marine deposits were largely withdrawn from 

 the area of the present land surface of the globe, which events have 

 in general furnished the basis for what are regarded as the systemic 

 rock and time boundaries of geology. If this possibility could be 

 proved it would help to explain the numerous examples of extinction 

 and evolution that emphasize the geologic time table, and it would 

 obviously leave few available marks in the record of life or in the 

 sediments now available for study. 



I have always been intensely interested in this subject, as who has 

 not? Circumstances have, however, kept me rather fully occupied 

 with the Mesozoic and Cenozoic floras of lower latitudes. Recently, 

 in working up some Eocene floras for the Geological Survey of 

 Canada — a subject which I approached while fresh from work on 

 the middle and upper Eocene floras of southeastern North America — 

 I was much impressed with the total dissimilarity between these Cana- 

 dian floras, which are a part of the so-called Miocene- Arctic flora of 

 Alaska, Greenland, Iceland, Spitzbergen, etc., and the contempora- 

 neous flora of our Gulf states. This led to a general survey of the 

 subject, some of the results of which are presented in the following 

 notes. 



It may be mentioned parenthetically that both paleozoology and 

 paleobotany have suffered the drawbacks incident to the fact that their 

 chief cultivators have been resident in the North Temperate Zone. I 

 do not recall a single paleobotanist who has had a first-hand ac- 

 quaintance with the tropical floras of the present. The same state- 

 ment is to a very great extent true of paleozoologists, and I gravely 

 question whether those who cultivate the field of invertebrate pale- 

 ontology concern themselves greatly with the results of recent re- 

 searches in oceanography and their bearing on problems of distribu- 

 tion in the past. 



After seeing the sub-tropical existing flora of southern Florida, 

 the tropical flora of the Antilles and Central America, and the tropi- 



2 Generally recognized to be of upper Eocene age in recent years. 



