PEALE.] 



RESUME — MESOZOIC ROCKS JURA TRIAS. 



623 



been identified by Prof. C. A. White as Triassic (?). Their resemblance 

 to beds at Station 66 was apparent, and they were considered to be of the 

 same age while we were in the field. 



Blackfoot Basin. — In this region the Triassic beds are generally con- 

 cealed by the overlying Jurassic limestones and shales. At Station 66, 

 however, and in several of the ridges in the immediate neighborhood, 

 as at Station 70 and various points in the northern spurs of the Preuss 

 Eange, we have the lower division showing. 



Bear Lake Plateau. — Towards the northern end of the Bear Lake Plat- 

 eau the Triassic red sandstones appear in folds under the almost hori- 

 zontal layers of the Wahsatch Group. These beds, with the overlying 

 Jurassic, continue northward to the Preuss Eange. 



Sublette Range. — The eastern slopes of the Sublette Eange are almost 

 entirely of Jurassic rocks. On the west, however, the Bed Beds show. 

 The lower group does not appear as far as noted by us. 



Jurassic. — The localities given for the Triassic might be given also as 

 Jurassic localities, and I shall therefore not repeat them here, but refer 

 the reader to the preceding chapters. 



The Jurassic strata are conformable to the underlying Eed Beds. I 

 have divided them into two groups, which I have named after the fossils 

 that appear to be characteristic of them, at least as far as the district is 

 concerned. 



The lower group consists mainly of blue and gray limestones which 

 become shaly towards the top of the section. Pentacrinus asteriscus ap- 

 pears to range through the limestones from top to bottom. The upper 

 group is mainly arenaceous, and at the locality of the best section, con- 

 tained Belemnites densus, from which I have named the group, although 

 it is probable that Belemnites extends down in the formation, and will 

 be found associated with Pentacrinus. 



The following is the general section of the Jura-Trias of the district 

 examined by us : 



General section in Southeast Idaho and Western Wyoming. 



i. 



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4. Eed and gray shales with green sandstones, and arenaceous 

 limestones at the upper portion of the section, capped by 

 a quartzite that is probably the base of the Cretaceous.' 



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3. Laminated limestones, blue at base, passing into gray at 

 toj), succeeded above by grayish calcareous shales; many 

 of the layers are probably arenaceous. 



O 



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CO 



GO 



Q 

 S 



a 



a 



2. Eed quartzitic sandstones with shaly arenaceous and cal- 

 careous layers at the base of the section. These are 

 probably the equivalents of the typical Eed Beds of the 

 Eastern Eocky Mountain region. 



CD 

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Pi 



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1. Alternations of reddish and greenish sandstones and arena- 

 ceous and calcareous shales with blue and gray laminated 

 limestones. These beds are fossiliferous at four horizons, 

 containing species of a new Triassic t genus by Professor 

 Hyatt, together with forms that have been heretofore 

 considered as of Jurassic age. 



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