ee ee ee 
W. M. Fontaine—Mesozoie Strata of Virginia. 237 
the east have spread laterally, so as near the border of the 
Azoic, to have coalesced into one sheet. he facts observed 
rather favor the latter method of advance. From this suppo- 
It is probable that the courses of the present principal 
Streams were marked out by this ice action, and hence come 
their direct course and independence of the character of the 
i fl 
reach the eastern slopes. t the same time the greater exten- 
sion of the Gulf waters northward would cause southerly winds 
to sweep over these slopes. e winds passing over the cold 
know must have existed. This condition of things would also 
have been eminently favorable for the production of coal. This 
was only brought to a close in the final advance of the ice at 
the end of the Jurassic Period, when all the abundant forms of 
plants of that period were extinguished to ) mo 
o other cause seems adequate to explain the total extinction 
of the Jurassic flora, and the complete change which we find 
im the succeeding Cretaceous flora. ; 
But while the plants were growing in the lowland and around 
the lakes, a very different condition of things prevailed in the 
high Appalachians. The stratigraphy of the formations com- 
posing this belt, and the amount of erosion which, as we know, 
took place, make it clear that in the early Mesozoic times 
much of this region must have stood above the snow line, and 
a still larger portion near it. If we recall the physical features 
of the North American continent which existed at that time, 
we shall see that even with our present climate then prevailing, 
the conditions would have been eminently favorable for the 
