> 
198 B. N. A. BOUNDARY COMMISSION, 
plant beds of the former locality being overlaid by some hundreds*—in 
the latter by several thousand}—feet of beds, with well-marked marine 
Cretaceous forms. Prof. Newberry, also,—as pointed out by Cope,f— 
though so familiar with the plants, is himself obliged to appeal to the 
evidence of the animal remains to fix the age of the deposits ; the plants 
not being sufficiently closely comparable with the European. Nor does 
the wide difference of opinion, with regard to age, of two so able 
paleontologists in this field, tend to inspire confidence in the flora as a 
guide. It would indeed appear, that the Cretaceous and Tertiary floras 
of America and Europe are not yet sufficiently known to enable their 
use as tests of age. The differences established between various locali- 
ties, and thought when only a small area was known to indicate steps in 
a general progress ; now seem to be due, to a great extent, to the replace- 
ment of one flora by another by migration, or to original differences in 
climate or condition, of the various places. 
456. In one respect, however, the plants appear capable of affording 
a useful addition to the evidence. If, as appears probable chiefly from 
their study, a well marked maximum period of warmth was co-incident 
with the early part of the Lignite formation, preceded and followed by 
cooler periods, represented by the Dakota and later Tertiary deposits 
respectively ; it may be possible to correlate this with the warm period 
of the early Eocene in Europe, and thus establish a direct synchronism. 
This carries with it additional probability, now that the possible depend- 
ence of such regular cyclical changes on astronomical causes, has been 
shown. 
457. Fresh-water molluscs, do not usually offer to the paleontologist 
a very safe criterion. They preserve, from their earliest known appear- 
ance, a wonderful similarity in genera and species; and their forms are 
longer lived than those of most animals, and from the nature of the 
shell and its ornamentation, changes which may be specific, are not 
so well defined or clearly recognisable as in marine shells. Specific 
relations, however, when demonstrable are of value, and it would appear 
that such exist between some, at least, of the molluses of the disputed 
beds of the west, and those of the eastern border of the Lignite forma- 
tion, the Tertiary age of which has only been in dispute since it became 
necessary for the preservation of consistency, to include it with the 
former in the Cretaceous. The general facies, however, of the fresh- 
water shells in so far as it may weigh, is certainly Tertiary. 

* Newberry. Am. Journ, Sci. and Arts., 
t Richardson, in Report of Progress Geol, Surv. Canada, 1872-73. 
t U. 8, Geol. Surv. Territ., 1873, p. 443. 

s Mee 
—— tS 
