422 T. W. STANTON 
corals, Rudistae, Actaeonella, etc., which suggest the Cretaceous 
of Jamaica. It may be considered a reef facies of the Ripley fauna. 
All the late Cretaceous marine faunas that have been briefly men- 
tioned are still typically Mesozoic, although it is true that they con- 
tain many generic types that continue on through the Tertiary. The 
succeeding Tertiary faunas, whether on the Pacific coast, the Gulf 
border, or the Atlantic coastal plain, show a very striking change 
from the Cretaceous faunas that immediately precede them. ‘The 
specific types are practically all different. 
Non-marine later Cretaceous faunas.—In the Rocky Mountain 
region throughout later Cretaceous time there was a great develop- 
ment of freshwater and brackish-water deposits alternating with 
marine formations. ‘They are usually coal-bearing, and yield inver- 
tebrate faunas frequently associated with land vertebrates and plants. 
The invertebrate fauna of the Dakota sandstone is too meager 
to be of much value. It consists of a few brackish-water species 
with Unio and a few other freshwater shells in other strata and at 
the top some marine species that probably really belong with the 
succeeding Colorado fauna. The freshwater species show relation- 
ship through the genus Pyrgulifera with the fauna of the Bear River 
formation which is apparently about on the horizon of, or a little 
later than, the Dakota. ‘The Bear River fauna is distributed over a 
considerable area in southwestern Wyoming, and is unique among 
western non-marine faunas in that it contains a number of types 
that have left no descendants in later formations of the region. ‘The 
most distinctive forms are freshwater species, but the fauna also con- 
tains brackish-water elements. ‘The submergence beneath the Colo- 
rado sea which immediately followed the deposition of the Bear River 
formation seems to have been so complete in this region that the fresh- 
water forms were not able to survive. But in the Colorado group itself 
along the western margin of the sea, especially in Utah and western 
Wyoming, there are intercalations of coal-bearing beds which contain 
a few Unios and other freshwater shells and brackish-water types 
like Ostrea, Anomia, Corbula, and Modiola, some of which recur 
in identical or closely similar forms at several horizons to the top of 
the Cretaceous. 
In the Montana group there are local more or less distinctive non- 
