WHITE. | LARAMIE FOSSILS. 51 
water mollusks with the fresh-water forms which characterize the Wah- 
satch and other purely fresh-water groups above the Laramie have yet 
been observed. But if sedimentation was continuous from the Laramie, 
to the Wahsatch Group, as it is believed to have been, we may reason- 
ably expect to find such a commingling of species at least in the lower 
strata of the Wahsatch Group or the top of the Laramie. 
Paleontologically the Laramie Group stands out clearly and dis- 
tinetly from the marine Fox Hills Cretaceous Group beneath, and the 
purely fresh-water formations above it, even though they may be con- 
nected by certain faunal types in the manner suggested. Its zodlogical 
characteristics are such also as to mark the Laramie as a well-defined 
period in geological history, apparently quite codrdinate in importance 
with all that portion of the preceding Cretaceous period, which is rep- 
resented by any and all North American strata which have been referred 
to that period. The stratigraphical relations of the Laramie Group I 
have discussed at length in the works already cited, and I need only eall 
attention here to the unique character of its invertebrate fauna, as ex- 
hibited in this article and the accompanying illustrations, not only as 
regards the relation of the latter to the faunv of the formations which 
respectively underlie and overlie it, but as regards any other known 
faune. The unique character of this Laramie fauna is not affected by 
the fact that a large proportion of its types, especially those of its fresh- 
water and land mollusks, are evidently the genetic precursors of some 
of those now living in North American fresh-waters, because compari- 
sons are made with that fauna in its entirety, and with it as regards its 
position in geological time. ‘There are other brackish-water deposits 
among the strata of that great western region, especially those of Cre- 
taceous age, but these are of comparatively small extent and contain 
limited faune the species of which at least are different from those of the 
Laramie Group, which latter fauna evidently lived in a great brackish- 
water sea. Those limited faune are mentioned here for the purpose of 
pointing out the fact that they are not to be confounded with the Lar- 
amie fauna, whatever genetic relations they may have sustained to it in 
fact, and in the order of time. 
The evidence as to the true geological age of the Laramie Group has 
also been discussed in the two former publications before cited, and there- 
fore only a brief summary of that question will be given in this article. 
Among the vertebrate remains that have hitherto been discovered in its 
strata are some of distinctively Cretaceous types as judged by European 
standard, namely, the Dinosaurian. Therefore vertebrate paleontologists 
have generally regarded the Laramie Group as of Cretaceous age. Paleo- 
botanists, however, have quite as generally regarded the vegetable re- 
mains of the group as belonging to Tertiary types. Among all the inver- 
tebrate fossils which have yet been discovered in the strata of the Lara- 
mie Group, none of the types are distinctively characteristic of the Cre- 
taceous period according to any hitherto recognized standard. Many 
of the molluscan types of this group still exist, although the species are 
of course extinct, and some of those types are known to have existed. 
during the Cretaceous epochs preceding the Laramie. But on the other 
hand four or five molluscan genera and subgenera have been recognized 
in the fauna of the Laramie Group that are not known beyond its limits. 
In view of the fact that the known Cretaceous flora of North America 
has near affinities with European Tertiary types, some persons regard 
the Tertiary facies of the Laramie flora as presenting little objection to 
a reference of that group to Cretaceous age. To those who hold such 
views the balance of paleontological evidence seems to be in favor of 
