178 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



J. W. Dawson has extended this conclusion as to the arctic 

 origin of the Tertiary floras to those of more ancient periods, 

 and concludes that the Silurian, Devonian, and Carbonifer- 

 ous floras all entered the North American continent from the 

 northeast, and that within the arctic circle was the great 

 nursery in which the successive vegetations, from the oldest 

 to the most recent, had their origin. 



ANCIENT ARCTIC CLIMATE. 



Dawson supposes that the subsequent change in climate in 

 these northern regions was'geographical rather than cosmi- 

 cal, and that the arctic climate at the sea-level, as long taught 

 by the present writer, never attained the point of glaciation 

 until the end of the Tertiary time. 



In like manner, J. F.Campbell, abandoning his former views 

 of a great ice-cap, now concludes that no geological record 

 exists of any abnormal glacial periods colder than the world's 

 climate of to-day. Geographical changes affecting the rela- 

 tions of sea and land, and elevating portions of the earth's 

 surface into regions of the atmosphere where perpetual frost 

 prevails, will, according to him, account for all the phenomena. 



SUPPOSED DISPLACEMENT OF THE EARTH'S AXIS. 



J. W. Dawson calls attention to the well-known fact that 

 not only the movement of successive floras in this continent, 

 but the directions of the great accumulations of sediment 

 throughout all these periods, as well as the great lines of 

 plication of the strata, which depend upon these, coincide 

 with the direction of the polar currents of to-day, and remarks 

 that all these facts go to refute the notion, which has lately 

 been resuscitated, of a change in the position of the earth's 

 axis of rotation a view which, however conceivable to the 

 astronomer and the physicist, cannot be admitted by the 

 geologist, who sees, in the facts already set forth, the evi- 

 dence that no considerable change of that kind can have taken 

 place since the beginning of Paleozoic time. Polar currents 

 seem to have been in all ages the potent agents in transport- 

 ing the debris of older rocks towards the equator; while, on 

 the other hand, as remarked by Dawson, the great organic 

 limestones, which represent the contemporaneous food-bear- 

 ing warm currents from equatorial regions, were deposited 



