teaue.1 RESUME— MESOZOIC EOCKS — JURA-TRIAS. 625 



Dr. White says : 



Among the exposures of Jura-Trias strata in the district here indicated (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 coutain 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. 



Professor Hyatt proposes one new genus, which has not only important and signifi- 

 cant relations with other genera, but the fact is an interesting one that with its first 

 and only discovery three strictly conforming, but well-differentiated species, were found 

 associated together, indicating thereby the permanent establishment of that generic 

 form. 



According to European standards, the Cephalopods here described are unquestiona 

 bly of Triassic types, and, as pointed out by Professor Hyatt, * * * they have more 

 resemblance to certain Cephalopods of the Muschelkalk of Europe than to any other. 

 This is an interesting and somewhat rmexpected circumstance, since the only other 

 Cephalopod forms from strata of the Western Territories which have been assigned to 

 the Trias as distinct from the Jura have been regarded as especially representing the 

 horizon of the Saint Cassian Aussee and Halldstadt deposits of Europe. 



The fossils here referred to by Dr. White are described by Professor 

 Meek in Yol. IV Eeport U. S. Geol. Exploration of Fortieth Parallel. 

 They are from the Star Peak Group of Western Nevada.* 



King, in speaking of this group, which he calls the Alpine Star Peak 

 Trias, says : 



It will be remembered that the Trias east of the Wahsatch is also stratigraphically 

 divided into two prominent parts of nearly equal volume ; the lower red-beds, which 

 contain little or no limestone, and but few isolated beds of gypsum, and the Upper 

 Red Bed, which are characterized by occasional limestone seams of no great volume, 

 and frequent occurrences of gypsum. These two Triassic seas, separated by a wido 

 area of continental land, differ from each other in a manner which renders correlation 

 next to impossible. If there is any correlation between the beds of the two series, it 

 would seem probable that the Koipato is the equivalent of the Lower Red Beds of the 

 eastern sea, and that the overlying Star Peak Group may be the equivalent of the 

 Upper Red Beds, the two being characterized by intercalations of limestone.t 



Our district is intermediate between the district here referred to by 

 King and the eastern seas mentioned by him, and it is difficult to corre- 

 late the sections lithologicaHy. We have, however, calcareous layers 

 in the Bed Beds (No. 2 of the section), and if the fossils from the Star 

 Peak Group are Upper Trias, and those from No. 1 of our section are 

 the equivalent of the fossils of the Muschelkalk of Europe, we may, per- 

 haps, indicate the correlation as follows : 



King's Section. Section in Southeast Idaho, &c. 



Star Peak Group = Eed Beds. 

 Koipato Group == Meekoceras Beds. 



Whether the Meekoceras Beds should be considered as of Lower or 

 Middle Trias cannot, of course, be stated as yet. The Nevada section 

 has a much greater thickness than our section, which is, however, greater 

 than that of the Colorado section. 



It is possible that a portion of the beds referred to the Upper Division 

 of the Carboniferous in some portions of the West may yet be found to 

 be in part at least equivalent of the Meekoceras Beds. In settling some 

 of these doubtful questions, there is scarcely any portion of the West that 

 will afford a better ground for study than the district rapidly gone over 

 by us in 1877. 



The following is a complete list of the Jura Trias fossils collected by 

 us and identified by Professor White : 



* U. S. Geol. Exploration of the 40th Parallel, Vol. II, chapter V; Vol. I, p. 269. 

 - Ubid., Vol. I, p. 270. 



40 G s 



