190 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 faunas. — 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. 



1 Mesozoic Fossils, Vol. I (1879), PP- 186-90. 



2 Proc. Cal. .4 cad. Sci., 3d Ser., Vol. II (1902), p. 59. 



