ST. jom.] MESOZOTC AEEAS TRIASSIC. 493 



include in the latter the deposits here referred to, which embrace a thick- 

 ness of about 2,000 feet, the depositions of the period underwent marked 

 change in their lithological appearance and the nature of the compo- 

 nents — indeed to such an extent as to render the term red beds of no de- 

 scriptive significance in this quarter. The appearance presented by the 

 horizon here alluded to is shown in the section across this ridge at a 

 point but a short distance north of our southern boundary, a description 

 of which has been given in a preceding page. 



A few miles to the north, however, in the vicinity of Station IV, there 

 occurs a set of red sandstone strata and deep-red. arenaceous shales, 

 underlaid by a heavy ledge of coarse, conglomeritic, quartzitic red sand- 

 stone, which, hthologically, bears marked resemblance to portions of the 

 '•red bed" series. But the details of the structural complications ac- 

 companying these deposits at the latter locality have not been suffi- 

 ciently investigated to warrant a more definite statement of their strati- 

 graphical relations than that based upon lithological resemblances. And, 

 so far as lithological appearances may be relied upon, the reddish sand- 

 stones to the southwest and northwest of Higham's Peak (Station V) 

 might be compared with the Triassic " red beds," only these deposits oc- 

 cur outside of and apparently overlying a belt of limestones whose fos- 

 sils are probably allied to Jurassic forms. Hence, in regard to the 

 horizons of this period in the southwest portion of the district, I can 

 speak with any degree of confidence only of the section above mentioned, 

 which crosses this ridge near our south line, and where the " red beds," 

 as such, are scarcely recognizable lithologically. 



The examinations in these deposits in the basin ridges west of John 

 Gray's Lake merely recognized their presence as heavy beds of red sand- 

 stones and sandy shales, while in the vicinity of the Blackfoot Bange 

 only remnants of the formation were met with. But in the Caribou 

 Bange the Triassic deposits are developed under their ordinary phases, 

 and, as seen along the northeast flank of the range, they may attain an 

 average thickness. In this quarter it was found to be in many instances 

 difficult to distinguish between these deposits and a series of red sand- 

 stones and shales which belong to a later formation, overlying or inter- 

 bedded with limestones containing Jurassic fossils. Such is the case in 

 the mountain block between Fall Creek and Pyramid Creek, and, unless 

 these deposits reach an enormous vertical thickness at this locality, it 

 may be questioned whether the red sandstone forming the crest of Sta- 

 tion XXV ridge is not a member of the Jurassic rather than of the Trias. 

 To the northwest of the latter point the space occupied by these de- 

 posits probably does not exceed 1,500 feet, and it may not be above 

 1,000 feet. Above the latter locality the Trias gradually declines in the 

 present mountain border, being confined to a narrow strip adjacent the 

 valley and not well exposed at the points visited south of McCoy Creek; 

 this, of course, assuming that the rusty-red sandstones and shales and 

 intercalated limestones at the latter locality and vicinity pertain to the 

 Jurassic. Bocks of this age were not recognized in the wider belt extend- 

 ing over across to the southwest base of the range at any part within 

 our territory. 



The Trias is much more prominently displayed in the Snake Biver 

 Bange, and may be traced for indes by its color characters, its outcrop 

 funning a narrow belt of variable width, extending from the Pierre's 

 Mountains in the northwest to the low mountains south of Teton Pass, 

 whence they probably extend down to the Snake Biver in the vicinity 

 of the upper entrance to the Grand Canon. In the immediate vicinity 

 of Station XL this horizon is well exposed, consisting of heavy deposits 



