366 C. A. White—Fossil Faunas and Floras. 
the Laramie up into the equivalent of the Wasatch, and perhaps 
also into that of the Green River Group.* 
This result of those studies makes it necessary to deny the 
correctness of the claim, which certain authors have made, 
that there was an entire stratigraphical break in the series re- 
ferred to at the close of the Laramie period. Still, it is not 
denied that the Wasatch strata usually, if not always, rests 
unconformably, if at all, upon the strata which have been 
called the Bear River Laramie; and in some cases also upon 
other Laramie strata. In short it is admitted that the area of 
continuous sedimentation was materially restricted at the close 
of the Laramie period; but it was not wholly interrupted until 
the close of the Bridger epoch. 
Besides the recognition of proof that sedimentation was con- 
tinuous through the whole vertical range of this intra-conti- 
nental series of deposits within at least certain portions of the 
area they occupy, the studies referred to have resulted in show- 
ing that certain of the species of the fresh-water gill-bearing 
mollusca of the Laramie period survived into the Wasatch 
epoch and became an integral part of the then existing purely 
fresh-water molluscan fauna.+ ‘Furthermore, it is well known 
that certain other molluscan species range through the whole 
fresh-water Hocene series, from the Wasatch to the Bridger 
Group, inclusive. Again, Professor Lester F. Ward has shown 
that more than twenty species of plants are common to the 
Laramie and Green River Groups; thus indicating that a large 
proportion of the species of the Laramie flora long survived the 
close of the Laramie period and mingled with the floras of the 
succeeding epochs. 
Here then, we have what is regarded as satisfactory proof 
that the stratigraphical series is complete from the Laramie to 
the Bridger Group, inclusive. And yet within the vertical 
range of that series the remains of several distinct land verte- 
brate faunas are found, which are not only widely diverse 
in their characteristics, but seem to have been introduced 
and extinguished with a suddenness that has left us with little 
or nothing learned concerning either their ancestry or their 
progeny. Indeed, a considerable proportion of the fossil verte- 
brate faunas which have been discovered in the North Ameri- 
can Mesozoic and Cenozoic strata are so clearly defined from 
one another by their own distinguishing characteristics that 
they appear to have been suddenly introduced and as suddenly 
extinguished. Moreover the differences in the characteristics 
* See Bull. U. S. Geol. Survey No. 34, pp. 16,17; also this Journal, III, xxv, 
p. 411-413. 
+ Bull. U. S. Geol. Survey, No. 34. 
¢ Sixth Ann. Report Director U.S. Geol. Survey; table covering pp. 443-514. 
