u 
300 BOTANICAL GAZETTE. [| December, 
from the one to the other must have been very gradual, and have ex- 
tended over an immense interval of time; long enough, indeed, as Dr. C. 
A White has so clearly shown, for the transformation of a distinetively 
brackish water molluscan fauna toa fresh water fauna, without extine- 
tion of types It is in these peculiarities that lies the explanation of the 
difficulty experienced in attempting to correlate this formation with 
others probably deposited at the same time in different parts of the world. 
It would be extremely improbable that precisely similar conditions should 
prevail in widely separated localities cut off, as we know they must have 
been, by barriers of both land and water that existed at that time. 
In order to ascertain what answer an exhaustive examination of the 
plant remains would be able to give to the question, Prof. Ward has pre- 
pared an elaborate table, in which are compared ‘all the known species 
found in the Senonian, Laramie and Eocene formations. The result 
shows that the Laramie flora resembles the one about as much as the 
other, which in itself proves nothing; but in the discussion which follows 
the table it is concluded, in a manner satisfactory to the author, at least 
that it has a stronger S:nonian than Eocene facies. This is because more 
important types extend from the Senonian into the Laramie, and when, 
as it is well known, the vegetation was less diversified than later The 
flora of the Laramie period is perhaps no more remarkable than could 
be accounted for on the ground of the peculiar conditions which obtained 
at the time of its deposition. Its isolated character, its change from a 
brackish toafresh water dep sit, are sufficient to impress upon ita sttons 
individuality. This examination shows more plainly than ever that the 
whole discussion resolves itself into 1 mere question of a name, and what 
this shall be is not of as much importance as might at first be anticl 
pated. 
_ This discussion is followed by the systematic portion of the paper 
which deals with the results of the personal observations of the author 
upon the flora of this group. This isin the form of a list, unaccompanied 
by , escriptions, of the type or representative species detected in the col- 
lections made by Prof. Ward in Colorado, Wyoming and Montana. The 
descr’ ptions and discussions of species are to be found in a later work, 10 
which this list is but supplementary; and, indeed, both papers #T¢ “i 
signed as an introduction to the larger monograph which the author as” 
in preparation. 
The illustrations, which are by the photo-lithographic proces 
among the best of the kind that we have seen. 
n as a whole, this paper must be regarded as one 
are 
of the most 
valuable contributions that have been made to the discussion of the Lan 
mie group.* 
Types of the Laramie Flora. By Lester F. Ward. Bulletin of the U 8. . 
Geological Survey, No. 37.. Washington, 1887. Pp. 1-115, pl. ! oo 
In this paper the species given in a list in the former work ar © — 
