418 T. W. STANTON 
Morrison formation and in others on older formations down to the 
Carboniferous. They are always directly overlain by the Dakota 
sandstone. 
Early Cretaceous freshwater jaunas——The Morrison fauna which 
may possibly be Cretaceous has already been referred to in discussing 
the Jurassic. The coal-bearing Kootenai formation of southern 
Canada and Montana which is determined by its stratigraphic posi- 
tion and by its flora to be Lower Cretaceous has yielded a few Unios 
and freshwater gastropods, mostly of simple modern types. These, 
like the similar forms in the Morrison, are interesting chiefly from 
the fact that they were probably the direct ancestors of some of the 
modern American freshwater forms, their successors having been 
preserved in the rivers of the adjacent land whenever the larger area 
previously occupied by them was submerged in the sea. 
LATER CRETACEOUS FAUNAS 
Chico fauna.—On the Pacific coast the Horsetown fauna is suc- 
ceeded by the littoral Chico fauna which is distributed from the Yukon 
River to Lower California, occurring on the lower Yukon, the Alaska 
Peninsula, Queen Charlotte and Vancouver islands, in middle and 
southern Oregon, in the Sacramento valley and the coast ranges of 
California to San Diego, and on the peninsula of Lower California 
as far south as latitude 31° 30’. There are considerable local varia- 
tions in this fauna as would be expected in view of its great range 
in latitude. The assemblage of forms found on the Yukon is quite 
different from that occurring in the Sacramento valley, and still 
another facies is found in southern California, but these are all con- 
nected by common species so that there is no hesitation about referring 
both the northern and the southern facies to the Chico fauna. ‘The 
fauna as a whole, like the later Horsetown fauna, is Indo-Pacific in 
its affinities, and is strikingly different from the faunas of the Atlantic 
border and interior regions of North America. Whiteaves' and F. M. 
Anderson? have argued for a connection during Chico time between 
the Pacific and interior seas, but the evidence brought forward in 
support of this view is based on types that have a world-wide distri- 
bution and on those that are only similar, not specifically identical. 
t Mesozoic Fossils, Vol. I (1879), pp. 186-90. 
20Proc. Cale Aicad-19G1.. 2d Sei jeV Ol. la(Go2)) mp :a50: 
