Cretaceous floras isolated. ] a ee ee ‘ f 
are identified in the Cretaceous of Germany, none in the Dakota group, which has 
species of oaks of a different type. Of the Lawrinee, Greenland has seven ; we have 
seventeen in the Dakota group; Europe has none, while species of Credneria are 
numerous in the Quader sandstone of Germany, and one only has been described 
from Greenland and one from the Dakota group. The same differences are observed 
in some of the other groups, while some present a remarkable degree of affinity. 
The same remark is applicable to the distribution of the plants upon the land 
surface of the formation in North America. Kansas, for example, has many species 
which have not been found in Nebraska or in Colorado, and vice versa. Inthe small 
number of species described here below from Minnesota, there are eight which have 
not been found elsewhere and are considered asnew. The geographical distribution, 
as far as it is known at the present time, is really more complex and varied than it 
is in the vegetation of the present epoch. The vegetable remains are not found 
strewn over large surfaces of the land, as if they were derived- from forests of wide 
extent, but over small isolated areas, more or less distant from each other, as if the 
leaves found there had fallen from groups of trees growing separate upon small 
islands or around wood swamps of small extent. And generally the plants of each 
area are of the same or of related species or represent only few species or genera, 
each locality having some plants proper to it. At one place the Sassafras abounds ; 
at another the Laurinew; still at another the Liriodendron, or species of another 
genus or family. Such a distribution does not agree with what it should be for 
plants derived by evolution of one or more species, as the plants of the same kind or 
varieties should, of course, remain together or follow the same range and direction 
in their distribution. It is worth remarking that as far as it can be observed neither 
the geological features nor the conditions of the atmosphere of the Middle Cretaceous 
have been subjected to great changes. The cataclysms caused by volcanic agency, 
and the gradual elevation of the chain of the Rocky mountains, have come after the 
Cretaceous. Nothing in the vegetation of that epoch indicates great and prolonged 
disturbances of the atmosphere. In the lower series of the vegetable scale, the ferns, 
the conifers and the Cycadew are of the same type and some of the same species, as 
in the Wealden, the Vernsdorf shale of the Lower Cretaceous, the schists of Korne, 
and those of the Cenomanian of Atane in Greenland. And from the time when 
the dicotyledonous plants appeared, or when we find them predominant, some 
of the types which may be called primitive, as it is not possible to refer them by 
derivation to some anterior ones, have continued in the different groups of floras 
through the Upper Cretaceous and the Tertiary to the present epoch, modified, indeed, 
but distinct enough to be recognized in many genera and species of the living flora 
of this country. 
