28 LL, Lesquereux on the Origin and Formation of Prairies. 
invaded at once by a peculiar kind of vegetation, especially by 
trees? Along the Ohio canals, the exposed Drift remains abso- 
lutely sterile in the first years after its denudation. By and by, 
some seeds of the plants growing in the neighborhood, those of 
the Mullen especially, invade this new soil, and become for a time 
its predominant vegetation. Afterward, a few shrubs, also the 
most common in the vicinity, appear on it; and it is only long © 
years after, and when the surface of the original ground is © 
already covered by a coat of vegetable mould, that a few trees, — 
the Black Locust, the Elm, etc., are seen here and there growing — 
up among the bushes. 
Prof. Winchell again says: ‘4th, The living germs of the dilu- 
vial deposits were buried during the glacial epoch ;” and, “5th, Jn 
proportion as the diluvial surface became exposed, the flora of the 
pre-glacial epoch was reproduced. . 
The author supposes that the vegetation which characterized 
the close of the Tertiary period was probably nearly identical 
with that existing at the present day under the same climatic 
conditions.” The climate of the Tertiary period at our latitude 
was evidently warmer than it is now, and, in the supposition of 
the author, we must expect of course to find the seeds of northern 
species, brought with the Diluvium and established with us, tak- 
ing the place of those destroyed by the influence of the glacial 
period. Considering only the general character of the flora of 
the Tertiary at different latitudes, it agrees well enough with this — 
idea, and we may give here some details which tend to strengthen 
the hyp a more, perhaps, than any reason advanced by the 
mself. 
author hi 
The Tertiary flora of Iceland, at least what is known of it, 
is more clesely related to our present flora than that of the Ter- 
tiary of the Mississippi. Among twenty-seven species of Phe- — 
nogamous plants,” it has eight Conifers, one of which, the most 
common, is an Araucaria ; two Pines, one of them related to _ 
Pinus serotina Michx. of ours; five Firs, one also related to our _ 
Hazelnut, ene Qak, whose nervation resembles that of our Quer- | 
cus montana Willd.; ene Buttonwood (Platanus), one Dombey- 
opsis, a genus of the Linden family, represented only by broken, 
scarcely determinable leaves; one Maple, apparently the most 
predominant species in that Tertiary flora of Iceland. and re- 
mar —_ by its large leaves and large fruits; one Grape, rela- 
_ to Vitis vulpine L. of ours; one Tulip tree, one Buckthorn, _ 
* This Journal, Lc, p. $37. ** 0. Heer: Flora Tert. Helvet, iii, 117. 
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