Part: 
Geologie Evolution, theoretic Considerations and Statistics 
on the Distribution of North American Plants, 
Chapter I. Cretaceous and Tertiary Floras, 
Beginning of the actual Flora. The history of the flora of North America, 
as it concerns this book, begins with the Cretaceous period when the 
land and water stood in a vastly different relationship than they do at present. 
That the subsequent shifting of the continental areas with respect to the 
oceans had great influence on the evolution of plant form and the 
of species cannot be gainsaid. It is beyond the province of this work to eal 
with the speculations upon this subject, but it will suffice to refer to such facts 
as bear upon the subsequent distribution of plant life in North America. 
The dicotyledonous angiosperms, which at present form the predominant 
vegetation of North America, occur in the beginning of the upper Creta- 
ceous, or at the close of the lower Cretaceous. The reign of the cyads and 
pines holds throughout the lower Cretaceous. If we examine a geologic map 
of the North American continent, we find that the northern and central part 
of the continent was cut off from South America by a sea, which covered 
Mexico and connected the Atlantic and Pacific oceans (see Fig. 1). The 
coniferous vegetation was, as paleontologic evidence shows, of the same 
general type all over the continent. In the upper Cretaceous more of 
Mexico was submerged and an arm of the American Mediterranean EX 
tending across the continent northward, covered the present states of Texas, 
New Mexico, Colorado, Kansas, Wyoming, Montana, etc. to the Arctic 
Ocean. It was then, the author believes, and not with the oncoming of 
the glacial period as TRANSEAU claims, that the beginning of the assort- 
ment of the coniferous vegetation into the eastern and western types or 
place (see Fig. 2, p. 172)... The upper Cretaceous period was sufficiently 
long to permit of the adjustment of the old types to the new environmental 
conditions and the evolution of new forms, for we have a great and sudden 
inswarming of the higher plants of modern types at the close of the lower 
