1903.] STANTON—MOLLUSCAN FAUNULE. 191 
fresh-water gastropods have been collected from beds immediately 
overlying the Cascade and referred by Mr. Weed to the Dakota, 
_ and these are of types different from any in the Harlowton collec- 
tion. That is, they are not specifically comparable. 
The Lakota formation is found in the Black Hills region, where 
it is said to overlie beds correlated with the Como beds, and to 
underlie the Dakota. It is characterized by a flora, by means of 
which its Lower Cretaceous age has been determined, and it has 
been tentatively correlated with a part of the Potomac and by 
inference also with the Kootanie and a part of the Glen Rose beds. 
It has yielded no animal remains, and therefore needs no further 
mention in this connection. 
Beds that have been referred to or correlated with the Dakota 
have a wider distribution than any of the other formations above 
mentioned. ‘The original area is in northeastern Nebraska on the 
Missouri River, from which the formation has been satisfactorily 
traced and identified through Nebraska and Kansas, where it 
covers considerable areas on the Great Plains. It consists of sev- 
eral hundred feet of coarse sandstone with some shales, passing up 
into the Fort Benton shales with evident continuity of sedimenta- 
tion. Paleontologically it is chiefly characterized by its large 
flora. It has yielded a very few marine and brackish water mol- 
lusca, but although it was evidently deposited at or near sea level 
it seems to have been largely non-marine in character, since a num- 
ber of localities in it have yielded fresh-water mollusca. The 
abundant land flora also indicates non-marine conditions. The 
fauna’ includes species of Unio, Margaritana, Corbula, Goniobasis, 
Viviparus and Pyrgulifera, none of which is specifically closely 
related to the species described In this paper. The Dakota has 
also been well identified in the Black Hills region and along the 
eastern base of the Rocky Mountains in Colorado. It has been 
mapped in many areas farther west in Wyoming, Montana, Utah, 
and elsewhere, but the correlation is certainly erroneous in some of 
these areas and must be considered doubtful in many of them, 
because the identifications have been based entirely on very gen- 
eral comparisons of the lithology and stratigraphy. It has been 
the general custom to refer to the Dakota any formation con- 
sisting in part of conglomerates and sandstones and underlying the 
1See C. A. White, « Notes on the Invertebrate Fauna of the Dakota Forma- 
tion,” Proc. U. S. Nat. Mus., Vol: XVII, pp. 131-138, 1894. . 
