m. 1.] WHITE ON JURA-TEIAS FOSSILS OF IDAHO. 107 



G, and H of tlie foregoing section as of Carboniferous age, although he 

 did not obtain any fossils from either of those three loAver members at that 

 locality, and he also thinks the horizon of these fossiliferous beds is be- 

 neath the so-called Eed Beds. The fossiliferous strata of the three locali- 

 ties herein especially considered contain all the new fossil forms which are 

 described in this paper, together with the three following identified spe- 

 cies, namely, Terebraticla augustaHall and Whitfield, Amculopecten Idaho- 

 ensis Meek, and Eumicrotis curta Hall. Ko other species besides these 

 and the eight new ones, and no other localities except the three specially 

 designated in foregoing paragraphs, will be considered in the present 

 paper, but it is intended that these strata, together with their equiva- 

 lents and associates in that region, shall be carefully studied at the 

 earliest opportunity. One object in presenting these few species only 

 in the present paper, is, that they embrace all the forms which are now 

 known to be associated with these interesting Cej)halopods of Triassic 

 type. 



From our present knowledge of the subject, it seems that the strata 

 containing the fossils herein described and noticed belong at or near the 

 base, of the series which in the Western Territories has latterly been 

 generally designated as the Jura-Trias, but it is noticeable that the Eed 

 Beds, which have been so generally assigned to the Trias, are wanting 

 here, although Dr. Peale now thinks they are present not many miles 

 away, and, as before said, that they occupy an immediately succeeding 

 horizon. It is probable that we may yet find satisfactory data for separa- 

 ting the strata which carry the fossils described and noticed in this paj^er, 

 together with their equivalent strata elsewhere, as distinctively Triassic, 

 fltom the other strata which have been so generally regarded as repre- 

 senting the Jurassic of EuroiDe ; but until more detailed studies can be 

 made, I prefer to use for all of them the provisional designation of Jura- 

 Trias. It is worthy of observation in this connection that none of the 

 well-known species which have been generally regarded as certainly of 

 Jurassic age, except Eumicrotis curta, occur associated with any of the 

 fossils embraced in this paper. It seems evident from Dr. Peale's ob- 

 servations that those well known Jurassic species occupy a higher hor- 

 izon ; and it also seems evident, from the frequent mention which E. 

 curta has received from the various geologists of the Western surveys 

 and explorations, that this species has a wide geographical and great 

 vertical range 5 and, furthermore, that it is associated with both Jurassic 

 and Triassic types. It should also be remarked that the Terebratula, 

 here identified, not without some doubt, as T. augusta Hall and Whit- 

 field, is referred by those authors to the Jurassic. 



According to European standards, the Cephalopods here described 

 are unquestionably of Triassic types, and, as pointed out by Professor 

 Hyatt in foUowiiig remarks, they have more resemblance to certain 

 Cephalopods of the Muschelkalk of Europe than to any other. This is an 

 interesting and somewhat unexpected circumstance, since the only other 



