Art. v.— Paieontologrical Papers ]¥o. 9: Fossils of 

 the Jura-Trias of Southeastern Idaho. 



By C. A. Tl^Biite, M. D. 



In Soiitlieastern Idaho and tlie adjacent portion of Wyoming, numer- 

 ous exposures of strata are reported by the field-geologists, which are, 

 or are assumed to be, equivalent with those Avhich, in the Western Ter- 

 ritories, have, by common consent, been assigned to the Jurassic period, 

 or, more recently, they have received the designation of Jura-Trias, in 

 consequence of the growing opinion that no paleontological plane of de- 

 markation exists among those strata of the Western Territories which 

 have hitherto been assigned respectively to the Jurassic and Triassic 

 periods. At a part of the localities above mentioned, some species of 

 fossils occur which have for many years been especially assigned to the 

 Jurassic, but those particular species do not occur with other fossils at 

 some of the other localities. The species referred to are, for example, 

 Fentacrinus asteriscus Meek and Hayden, Belemnites densus M. & H., 

 Eumicrotis curta Hall, Cmnptonecfes hellistriatiis M. & H., &c. At others 

 of the localities above referred to, notably those which are especially 

 considered in the following paragraphs, the fossils are mostly or entirely 

 of new species. 



Among the exposures of Jura-Trias strata in the district here indi- 

 cated (and they are numerous and comparatively small in consequence 

 of the great disturbance which they, together with their associated 

 strata, have suffered), there are three localities which are especially 

 interesting, because the strata there exposed contain not only a number 

 of new forms, but because some of the types in which those forms are 

 expressed are such as in Europe are regarded as characteristic of the 

 Trias. For convenience of reference, these localities are designated as 

 Nos. 1, 2, and 3. 



Locality Ko. 1 is in Idaho, about sixty-five miles north of the bound- 

 ary line between that Territory and Utah, about eighteen miles west of 

 the boundary line between Idaho and Wyoming, and about five miles 

 south of John Grray's lake. The region embracing this and neighbor- 

 ing localities has not yet been visited by myself, but Dr. A. C. Peale, 

 geologist of one of the surveying parties, in whose district for 1877 the 

 locality especially referred to occurs, has examined it brieflj", and fur- 

 nishes the data for the following section at locaUty No. 1, the member 



A Ibeing the highest of the series. 



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