of lowland, impassable barriers for Arctic plants, are possessed 

 of alpine species quite identical. These facts of discontinuous 

 distribution of mountain forms and their strong Arctic affinities, 

 many identical species recurring far to the north, demand an 

 explanation since continuous distribution is the common condi- 

 tion. We are indebted to Prof. Asa Gray for an explanation of 

 this interesting phenomenon, and the following paragraphs are 

 largely adaptations of his views to the case of Mt. Ktaadn. 



In the Pliocene epoch, in pre-glacial times, it is presumable that 

 a quite homogeneous and uniformly distributed flora encircled 

 the polar zone, there being then a postulated north polar land 

 connection continuous around the globe. Destroyed by some 

 great land movement, presumably toward the close of the Plio- 

 cene, only isolated islands, Greenland, Iceland, and others, now 

 remain to mark its probable former course. 



With the inauguration of the Pleistocene epoch great changes, 

 cumulative from the Pliocene, came about. Huge masses of 

 snow and ice, accumulated to the north and extended southward. 

 The cause of this accumulation, made possible by the lowering 

 of the temperature, is referred by Scott 1 to an epeirogenic move- 

 ment in northern North America, and the polar zone. Dr. 

 Chamberlin, 2 on the other hand, ascribes its cause to the gradual 

 depletion of CO 2 from the atmosphere by organic and inorganic 

 agencies, thus reducing the CO 2 blanket of the earth and facili- 

 tating radiation until the temperature became so lowered that 

 ice accumulation ensued. Whatever the theory of the cause, the 

 fact of glaciation remains the same. With the advent of ice 

 accumulation and refrigeration, this uniformly distributed Arctic 

 flora was driven southward in every longitude, retreating from 



1. Scott, W. B. An introduction to Geology. New York. 1899, p 524. 



2. Chamberlin, T. 0. A group of hypotheses bearing on climatic changes 

 Jour. Geo. 7 : 653-883. 1897. 



the ever advancing ice sheet. Our temperate flora was likewise 

 forced southward or exterminated by the glacial advance and by 

 the fleeing Arctic species. From this general consideration of 

 glaciation, we may now pass to its effect upon New England and 

 in particular Ktaadn. 



We have seen that as refrigeration progressed in the 

 polar zone the Arctic flora travelled to the southward, closely 



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