OC. A. White—Fossil Faunas and Floras. 365 
saurian remains of Cretaceous types, molluscan remains of both 
Tertiary and living types, and plant remains of both Tertiary 
and living species, have been found in such intimate associa- 
tion in strata of the Laramie Group as to indicate that they all 
lived contemporaneously. In another publication* I have 
shown that remains of living species of land mollusks have 
been found associated in the same strata with those of extinct 
genera and families of Miocene vertebrates. In still another,f 
I have shown that a fresh-water mulluscan fauna, nearly all 
the known species of which are closely related to living forms, 
has been found in Jurassic strata associated with a great variety 
of dinosaurian remains. 
The following remarks in support of the opinion just ad- 
vanced have reference to other cases which have been observed 
in connection with the great series of intra-continental strata 
which is found occupying a large region in the western part of 
our national domain; the vertical range of the series being 
from the Laramie Group to the Bridger, the uppermost of the 
fresh water Hocene Groups, inclusive. This series is one of 
unusual interest because of its intra-continental origin, of its 
great thickness and geographical extent for a series of such an 
origin, and of the importance of the fossil remains which have 
been collected from it. Indeed a large part of our present 
knowledge of the extinct land vertebrate life of North America 
has been derived from this series of strata; and yet that knowl- 
edge is strikingly imperfect and fragmentary. It is of course 
not strange that any record of extinct vertebrate life should be 
imperfect, but the broken character of this one is the more 
noteworthy because the record of both the invertebrate and 
plant life for the same series of strata and within the same 
region, seems to have never been wholly broken. Besides this 
evidence of the continuity of invertebrate and plant life in the 
series referred to, studies which [ have prosecuted in the field, 
and also among the collections which have from time to time 
been obtained from those formations, have disclosed satisfac- 
tory proof that for the whole series there was continuous sedi- 
mentation within a largearea.§ How large that area was has not 
been determined, but it is known to have embraced a consid- 
erable part of central.and northern Utah. 
It is probable also that in northeastern Montana and the 
adjacent part of Dakota, sedimentation was continuous from 
* Bull. U. S. Geol. Survey, No. 18, pp. 10-16. 
+ Bull. U. S. Geol. Survey, No. 29. 
} For a tabular exposition of the principal formations of the Rocky Mountain 
region, showing the relations of ee cones to other formations, see Ann, Report 
U.S. Geol. Surv. Terr. for 1876, p. 
§ See Bull. U. S. Geol. Survey, na 
Am. Jour. Sci.—THIRD SERIES, VOL. oe No. 197.—May, 1887. 
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