554 N. H. DARTON FISH REMAINS IN ORDOVICIAN ROCKS 



Shoshone canyon 30 to 35 miles east and south. Another dissimilar 

 feature in the section also is the presence of an overlying limestone 

 (Three forks) containing Devonian fossils. The Jefferson limestone ex- 

 tends along the various ranges of the Kocky mountains in central Mon- 

 tana, lying between the well denned Middle Cambrian limestone and 

 Devonian limestone or shales (Three forks) and having a thickness of 

 from 150 to 300 feet. Its color is dark, the bedding mostly massive, con- 

 stitution a dolomite, and the lower beds give rise to a prominent ledge or 

 cliff. In the Absaroka range, as described in the folio above cited, a few 

 poorly preserved fossils were found in the lower beds of the Jefferson 

 limestone, but they appeared to be species which "might occur high in the 

 Cambrian or near the base of the Silurian (Ordovician). In the same 

 way, at other localities, the species procured from near the summit of the 

 terrane are such as possess a wide vertical range and might be found as 

 low as the Silurian, but at the same time are known to occur elsewhere 

 with typical Devonian species." It has been suggested that the Jefferson 

 limestone may comprise a continuous series of sediments from Cambrian 

 to Middle Devonian in age, but in the absence of positive paleontologic 

 evidence its stratigraphic range can only be surmised. Perhaps a close 

 examination will reveal unconformities representing long time intervals. 

 However, it is possible or even probable that the Jefferson limestone in- 

 cludes the Bighorn limestone in whole or in part, and Ordovician fossils 

 will be found in it in some portions of Montana.* 



Ordovician in Western Wyoming 



During the examination of the Owl Creek Mountain region a few 

 observations were made on the east slope of the Wind Eiver range, where 

 the Bighorn limestone was seen occupying its usual position between 

 Deadwood and Madison formations. ]NTo detailed study was made nor 

 fossils obtained, but the limestone is 200 feet thick and presents its usual 

 characteristics, f Undoubtedly it is the same limestone that yielded 



* Descriptions of the Jefferson limestone are given in U. S. Geol. Survey folios 1, 24, 

 30, 52, and 56 ; Bulletins no. 110, pp. 25-29, and no. 139, pp. 37-38 ; Eighteenth Annual 

 Report, part iii, pp. 468-470, and Twentieth Annual Report, part iii, pp. 287-289. 



t In a preliminary examination of the Wind River range in 1906, I found the massive 

 silicious limestone member of the Bighorn formation west of Lander about 100 feet thick 

 and underlain by a thin bed of sandstone, partly calcareous, which contains large num- 

 bers of fossils. These have been determined as follows by Mr E. O. Ulrich : 



Receptaculites oweni, Hall ; Streptelasma cf. profundum, Conrad, and corniculum, 

 Hall; Ramose bryozoan, agreeing in general aspect with Callopora mtiltitabulata, Ulrich; 

 Plectambonites sericeus var. ; Dahnanella testudinaria var. ; Stropliomena n. sp. near 

 S. sulcata, Verneuil, and &. fluctuosa, Billings ; Ctenodonta cf. levata, Hall ; Cyrtodonta 

 cf. rotulata, Ulrich; Psiloconcha n. sp. ; Archinacella cf. A. deleta (Sardeson) and A. 

 subrotunda, Ulrich; Protowarthia cf. cancellata (Hall); Lophospira near L. elevata, 



