338 A. Winchell on the Prairies of the Mississippi Valley. 
period; but as their position is 120 feet below the ferruginous 
sands containing Megalonyx Jeffersoni, and as the nature of these 
species is incompatible with such a climate as we universally as- 
sociate with the glacial epoch, it is quite likely this assemblage 
of vegetable remains represents the general nature of the arboreal 
flora in existence near the close of the Tertiary period. 
Although our positive knowledge of the vegetation of the 
period immediately preceding the advent of the reign of ice is 
confessedly meagre, it is certain that all the facts in our posses- 
sion point to close specific correspondence with the modern veg- 
etation of the same regions—modified certainly by the fact that, 
even in the latest Tertiary, the climate was considerably warmer 
than in the same latitudes at the present day. 
(2.) The general eflect of the events which ushered in and 
marked the progress of the reign of ice was, to destroy the veg- 
egation flourishing over all the northern portion of the continent 
and mingle its forms with the cubic miles of debris detached from 
the underlying rocks. We find the trunks and limbs of trees 
buried 50 and 100 feet deep in this diluvial rubbish. It is im- 
ossible that myriads of vegetable germs should not also have 
een stored away. The drift deposits became the vast granery 
in which nature preserved her store of seeds through the long 
rigors of a geological winter. 
(3.) But what evidences have we that the seeds of plants are 
capable of retaining their vitality through a geological period? 
(a.) The ordinary process of destruction of vegetable tissues 
is merely an oxydation of the carbon and hydrogen entering 
into their constitution. It is seriously doubted whether the 
requisite conditions for such oxydation exist at considerable 
depths in the soil. It is stated that the piles sustaining the Lon- 
tained on piles driven 650 years ago, and they are yet perfectly 
Cedar, (Thuja occidentalis), bearing scarcely a trace of the wors 
ae Sent agencies upon them. Indeed it is known that 
