434 REPORT UNITED STATES GEOLOGICAL SURVEY. 



known species, they show strong resemblance to forms which occur else- 

 where in well-determined Jurassic horizons. In the wooded slopes to 

 the south and southwest of the station, belts of variegated pale red and 

 drab deposits are exposed in the secondary spurs descending from the 

 main ridges, the strata dipping off to the southeastward as far as coidd be 

 traced. The north spur descending to the plain exhibits successively 

 lower deposits, which, although it was impossible to ascertain their 

 thickness even approximately, occur in the following order: Immedi- 

 ately beneath the summit sandstone the north and northeast slope of 

 the station passes over a heavy deposit of deep red arenaceous shales 

 and thin layers of red sandstone which descend into the saddle connect- 

 ing this point with a lower nipple; the edges of these red beds and 

 overlying sandstone are also exposed in the northeast slopes of the next 

 west spur. In the crest of the nipple north of the station, shaly buff- 

 gray sandstone, overlaid by gray limestone, is seen, and thence to the 

 northward successive ledges of very hard reddish buff siliceous or sand- 

 stone beds appear, interbedded with drab and dark gray limestones and 

 red arenaceous indurated shales, dipping southwesterly at an angle of 

 20° to 30°, the hard ledges forming low crests along the gradually de- 

 clining spur. Near the foot of the ridge, and perhaps two and a half 

 miles north of the station, a heavy ledge of darkish drab cherty lime- 

 stone appears, rising obbquely to the general direction of the spur, and 

 dipping W. 5° S. at an angle of 20°. This ledge afforded a few speci- 

 mens of ' Zaphrentis and crinoidalremains, identifying it with the Carbon- 

 iferous. It will hence appear that the overlying siliceous beds, sand- 

 . stones, and interbedded red shales and limestones offer the same strati- 

 graphic series as that noticed in the Pierre's Mountains, north of Station 

 XL and south of Station XLII. 



It remains briefly to notice a remarkable but, unfortunately, obscure 

 exposure occurring in the southeasterly slope of Station XXXIX. This 

 shows a limited exposure apparently belonging to a heavy ledge of gray 

 limestone which stands nearly vertical, the top of the ledge bending 

 suddenly over to the southward, and otherwise showing what appears 

 to be the result of great disturbance. The apparent planes of bedding 

 show a strike E. 25° to 30° S. and W. 25° to 30° X., the planes steeply 

 dipping northward or nearly vertical. In the absence of other exposures 

 in the immediate vicinity affording the least corroborative evidence of 

 the existence of so sharp a fold in the strata at this point, renewed search 

 was made to discover whether or no the apparent bedding of the lime- 

 stone was to be attributable to deceptive cleavage, as remarked in con- 

 nection with the sandstone ledge in the near summit of the station, with 

 which the strike of the limestone certainly shows marked coincidence, but 

 •without more definite results. It is by no means of infrequent observation 

 in this region to find the heavier limestone deposits of both the Carbonif- 

 erous and Jurassic so changed and fractured by cleavage as to totally 

 obscure the true bedding of the ledges, which in many instances is only 

 determinable by noting the relation to associated strata which clearly 

 retain the original planes of deposition. But examining the country to 

 the eastward of Station XXXIX, in the belt of low hills intervening be- 

 tween this point and Teton Pass there occur in the crests of one or two 

 spur-ridges the edges of southwest-facing ledges which apparently dip 

 in the opposite direction, indicating a fold the axis of which cannot be 

 far removed from the ridge of which Station XXXIX forms one of the 

 western culminating points. 



The occurrence of the "red beds" and Jurassic limestone in the lower 

 portion of the valley of West Teton Pass Creek has already been alluded 



