A. P. Coleman — PaJeohotany, etc. 315 



Aet. ^IX.— Paleobotany and the Earth's Early History; 

 by A. P. CoLEMAX. 



Dr. Knowlton's paper on the ''Evolution of Geologic 

 Climates," read last winter before the Paleontological 

 Society, is full of interest to the ordinary geologist from 

 its comprehensive summing up of the ancient history of 

 land plants, such as only a master of the subject could 

 have produced. Part I of his paper rouses enthusiasm 

 with its splendid array of forests, mostly tropical, from 

 all parts of the world, culminating in the rich Eocene 

 flora. His account of the vegetation of the past confirms 

 and heightens the impression left by paleozoology that 

 during the greater part of the world's history tempera- 

 tures have been genial even in the far north and far 

 south where frigid climates now reign. Dr. Knowlton 

 suggests that not alone were the temperatures of past 

 ages warm, but that generally the climates were moist 

 with hothouse conditions and with no seasonal changes 

 until the latest periods. Annual rings are rarely found 

 in the trees and only once before the Pleistocene is a 

 period of severe cold admitted, in the early Permian time 

 of giaciation, and then the cold period ''was probably of 

 short duration," and did not affect North America, 

 Europe, or Northern Asia. 



Throughout this rapid outline of the successive floras 

 of the past there are few references to periods of cold or 

 of drought in the world's history, and these are mini- 

 mized, thus preparing the reader for Part II of the paper, 

 in which Marsden Manson's theory of the earth's ancient 

 climates as controlled by the earth's interior heat is ad- 

 vocated. 



A paleobotanist naturally lays stress on the equable 

 warmth and moisture of the earth's ancient climates, 

 since the plants themselves thrive best under such condi- 

 tions. In times of great drought or of extreme cold, such 

 as existed during eras of great land emergence, plants are 

 absent or rare and the chances of their preservation are 

 poor, so that the paleobotanist finds little or no evidence 

 of such severities of climate. The mild and moist 

 periods are tremendously emphasized and the relatively 

 short intervening periods of drought and cold are slurred 

 over or entirely unrecorded by Paleobotany. It is not 

 surprising, then, that the evidence of great cold and of 



