GEOGRAPHICAL DISTRIBUTION OF THE FLORA. 31 
explained by the supposition that no Middle Cretaceous rocks have been 
opened in districts where tropical or subtropical climatic conditions pre- 
vailed. This, however, is unsatisfactory, for the Lower Cretaceous rocks 
have been opened in all quarters of the world and plants have been col- 
lected from them; and the Dakota flora gives evidence from all sources 
that it is that of a warm temperate climate, and that the climate was in the 
same localities afterwards warmer, since palms, which may be accepted as 
an evidence of a warmer climate, are so abundant in the Laramie and 
Tertiary beds. 
From the conditions under which the Amboy Clays were deposited, 
that is, in estuaries of no great extent, surrounded by land covered with a 
dense vegetation, and from the nature of the deposits, largely fine clay 
which subsided in the quiet water, we should expect to find here the 
remains of herbaceous plants as well as arborescent, and yet so far they 
have been conspicuous by their absence. 
Again, we should have anticipated the preservation of insects in large 
numbers—dragon flies, at least, which were so numerous in the Jurassic 
age as to leave multitudes of representatives in the Solenhofen slates—and 
yet, though we have searched for them most carefully, no definite remains 
of insects have yet been discovered. Flowers were there in abundance, 
and why the insects have not left any proof of their existence is a mystery. 
That insects existed in great numbers as early as this is proved by the fact 
that in the St. Etienne coal basin in central France, in rocks of the Car- 
boniferous age, Mr. Charies Brongniart has obtained over 1,300 species of 
insects. 
GEOGRAPHICAL DISTRIBUTION OF THE FLORA. 
Tn this installment of fossil plants from the Amboy Clays, out of 156 
described species, about 50, or one-third of the whole number, are described 
by Heer from the Cretaceous rocks of Greenland. In Velenovsky’s Flora 
der Bohmischen Kreideformation I find 6 that I regard as identical with 
those that we have from New J ersey. In the Dakota group, out of 460 
described species, there are at least 40 which seem to occur in the Amboy 
Clays; and I have identified 3 positively, and several others presumably, 
