1894. PROCEEDTNGS OF THE NATIONAL MUSEUM. 137 



top of the formation, and that tliey lived in waters which were then 

 changing" to the marine condition which prevailed dnring- the sncceed- 

 ing Colorado epoch.* 



The invertebrate species collected by Prof. Mudgein Saline Conuty, 

 Kans., consist wholly of forms which are regarded as indicating a 

 marine habitat, bnt they are all sncli as are generally nnderstood to 

 indicate a littoral, or at least a sliallow water, condition. They were 

 described by Mr. Meek and myself, res])ectively.f I have never per- 

 sonally examined the stratigraphy of Saline Connty, Kans., bnt I 

 accepted Prof. Mudge's identification of the Dakota formation there 

 when I published the description of the species referred to, and I have 

 since expressed the opinion that the formation changes from a non- 

 marine to a marine condition in its southward and southeastward 

 extension.! 



Although the generic characteristics of all the forms contained in 

 the collection of Prof., Hicks are not well shown by the si^ecimens, I 

 have no reason to doubt the generic identity of anj- of them as indi- 

 cated by the names applied to them respectively in the foregoing- 

 descriptions. I therefore regard the collection as unmistakably indicat- 

 ing a nonmarine origin for the strata from which it was made. Indeed, 

 I think the character of the collection as a whole indicates a purely fresh- 

 water origin. This opinion is supi)orted by the following facts: Of 

 the five genera reprcvsented in the collection, representatives of three 

 of them, namely, Unio, (foniohasis, and Viviparus., have never been 

 found living in any other than fresh waters. It is true that species of 

 Gorhnla are usually found in saline waters, and often in those of full 

 marine saltness; but it is alsatrue that living species of that genus 

 sometimes range into fresh waters, and the fossil species have frequently 

 been found associated with Unio, Goniohasis, and VwiparuH. The fos- 

 sil faunal associates of Pyrgnlifera usually indicate a brackish-water 

 condition, but the tj'pe species of the genus, while sometimes found com- 

 mingled with shells of Ostrea, is oftener found associated with such 

 fresh-water forms as ZTnio, Viviparus, Campeloma., etc. Moreover, the 

 only known living species of the genus inhabit fresh waters. 



The general prevalence of land plants in the strata of the Dakota 

 formation is also an indication of its nonmarine origin, as is the gen- 

 eral absence of marine remains. Indeed, the only discoveries of fossil 

 remains in Dakota strata Avliich indicate a saline condition of the waters 

 in which they were deposited were made along a part of, or near, the 

 eastern border of the formation. 



I do not think it is fully proved that the bulk of that portion of the 

 formation which occurs in the Missouri Kiver valley in the vicinity of 



* Tliese remarks are based upon my recollection of a personal statement made to 

 me by Dr. Hayden. 



tVol. IX, U. S. Geo]. Sarv. Terr., pi. 2, pp. 80, 92, 109, 120,163, 164,170, 174, 195, 

 202, 253, 300, and 333; Proc. U. S. Nat. Museum, vol. 2, pi. 5, pp. 295, 296. 



tSee Bull. U. S. Geol. Survey, No. 82, p. 122. 



