230 FOREST LANDS OF NORTHERN RUSSIA. 



the forests must have been rich, varied, and vigorous in 

 their growth up to the immediate vicinity of the ancient 

 craters. It is not then in eruptive phenomena, whatever 

 violence we may attribute to them, that we must seek for 

 the true cause of the disappearance of the Arctic tertiary 

 flora. This was brought about exclusively by the climate, 

 the fall of temperature, at first almost nothing, then, 

 scarcely perceptible in the cretaceous period, gradually 

 increased, and from the time that it passed a certain limit 

 it brought on necessarily the retreat or the definite dis- 

 appearance of a multitude of species, which, up to that 

 time, had been the ornaments of the lands of the north. In 

 proportion, as this eliminatory process progressed, the 

 glaciers, the extension of which in Europe towards the 

 close of the tertiary period must have increased and 

 descended from the high summits, and finally overrun all 

 and effaced all. This invasion of the glaciers of the north, 

 an invasion not partial as in Europe but almost universal 

 or general, has been doubtless the proximate and direct 

 cause of the elimination of the later tertiary vegetation ; 

 or rather it should be said, the reduction of temperature 

 at once cause and effect, in promoting the extension of 

 the glaciers into countries evidently very moist, has contri- 

 buted by this very extension to intensify the cold, and 

 ultimately to transform the climate, so as to render it 

 incapable of promoting the vegetation of the greater part, 

 of plants, while by a kind of exappropriation the ground 

 stole away and came under their denomination.' 



There are embodied in these citations deliverances on 

 two perfectly distinct questions, in regard to which a 

 difference of opinion on either of which may exist without 

 affecting the conclusion to which one may have come upon 

 the other : the one relates to the course followed in the diffu- 

 sion of the plants specified ; the other relates to the cause or 

 occasion of changes of temperature of which this diffusion 

 may be considered an indication. It is the former alone with 

 which I am conversant, and which I desire more especially 



