

SOMMERS — FLORA OF NOVA SCOTIA AND COLORADO. 125 



these difficulties have been surmounted, and if we are yet very far 

 from a thorough comprehension of the subject, it cannot be said 

 that we have no data upon which we may construct hypotheses more 

 or less reasonable. We are in this respect following the proceed- 

 ings of the geologist, who supposes the dispersion of inorganic mat- 

 ter to have been produced by certain physical agencies acting upon 

 it. Nor can we do better than to accept his theories as explanatory 

 of our subject. 



The glacial theory which accounts for the phenomena of the drift 

 may afford an insight to the distribution of plant life upon this 

 continent ; it is said that the North American continent was more 

 recently glaciated than those of the Eastern hemisphere. Without 

 accepting this, we have evidence that the recession of this period is 

 more recent here, since its northern extremity is yet glaciated down 

 to the 70° of N. latitude at least. The physical condition of the 

 continent as low as the 36° of North latitude, i. e. from ten to 

 twelve degrees south of our present position, during the glacial 

 period, was such as exists now on the shores of the Arctic Ocean ; 

 the then existing climate of Colorado and the adjacent zone being 

 like that of Greenland in our epoch. 



Supposing the existence of plant life in abundance in our north- 

 ern region previous to the drift, a supposition which our coal 

 measures, &c. prove, we can easily estimate the influence of the 

 wave of congelation passing down from the north, would be to 

 disturb the atmospheric conditions to the extent of destroying the 

 flora in every locality invaded. But this process of ice formation 

 was no doubt like the other processes of nature, slow in growth, 

 not to be counted by decades or centuries, but by ages. Hence its 

 effects upon plant life were gradual in their development ; thus the 

 hardier species would remain for a time to struggle with ever in- 

 creasing adverse conditions, to be eventually destroyed or forced to 

 emigrate with their weaker brethren, being pushed forward by 

 every advancing wave of cold, so that in the final state of things 

 which obtained at the point of recession of the glacial era, the boreal 

 flora of America escaping annihilation, must have been driven 



