BT-JOHs.] TETON EANGE. 413 



a narrow ladder scaling the heights, the approximate direction east-west, 

 with a slight southerly inclination from the vertical. In the northeast 

 part of the range Professor Bradley remarked the occurrence, beneath 

 the Silurian limestones, of "a heavy body of dark micaceous gneiss, with 

 both granite and quartz veins," the metamorphics having a general south- 

 erly inclination, with, however, local northerly dips. Recognizing the 

 identity of certain peculiarities of weathering with these determined 

 gneiss exposures, which assume elaborate and beautifully carved sur- 

 faces, it appears that a large part of the east front of the range, as well 

 as a wide belt, if not the whole of the northwest expansion of the Ar- 

 chaean area, is composed of similar rocks. The distinctively granitic ledges 

 form the highest peaks of the range, as in Mount Hayden, peculiarly 

 massive heights, with smooth, sheer precipices and huge block-like but- 

 tresses, while in the Alpine basins and canon walls they appear in com- 

 paratively smooth surface-exposures, strongly contrasting with the gen- 

 erally sharp, highly- wrought sculpturing of the gneissic ridges. 



In the course of our examination, in the northern portion of the range, 

 a small area of Palaeozoic formations was brought to light, which rise up 

 on the northwest flank and cap the watershed for the distance of several 

 miles, when they are headed off by the sag at the head of the south 

 branch of the Xorth Pork of Pierre's Eiver, which also forms their 

 southern limits. On the west they are soon hidden by the upraised 

 volcanics, which latter sweep round the north end of the range and form 

 a continuous belt with similar volcanic deposits, which rise up on the 

 northeast flank of the range in the northern portion of Jackson's Basin. 



Ascending from the plain north of Pierre's Basin to a prominent ridge 

 at the head of the [North Fork of Pierre's River, occupied by Station 

 XXXII, the way for several miles passes over the laminated porphy- 

 ritic trachytes which here constitute the great outlying foreland of 

 the range, and which clip at a moderate and gradually diminishing 

 angle of inclination in the direction of the plain. Along the mountain 

 border they are suddenly terminated in irregular lines of bluffs, which 

 on the main Xorth Fork reach to within two and a half miles of 

 Station XXXII, where their elevation is about 2,000 feet above the 

 foot of the foreland. At this point the lowest of the sedimentaries 

 shows a thin-bedded drab limestone, indistinguishable, lithologically, 

 from the beds elsewhere found in connection with the Lower Silurian or 

 Quebec formation. In the opx>osite side of a lateral gulch half a mile 

 east, castellated exposures of heavy-bedded buff magnesian limestone, 

 showing a thickness of above 100 feet, are met with, the rock affording 

 a few Upper Silurian corals, Ealysites, &c. These ledges form a prom- 

 inent feature of the exposures in the steep slopes along the stream, and 

 are succeeded by the ordinary gray and drab, cherty limestones, with in- 

 terpolations of reddish siliceous deposits which make up a thickness of 

 several hundred feet, and affording in their contained organic remains 

 ample evidence of their Carboniferous age. The lower ledges are here 

 arranged in courses interbedded with shaly layers, and underlaid by softer 

 reddish deposits which intervene between the upper limestones and the 

 underlying magnesian limestone. Above, the limestones become thicker, 

 with siliceous interpolations, and often stained a pale red. Of these 

 Carboniferous beds there is probably exposed in the ridge of Station 

 XXXII a vertical thickness of 500 to 800 feet. In the summit these 

 beds dip 20° northwest; in the northwest spur their inclination slackens, 

 and toward the head of the before-mentioned lateral gulch the same 

 ledges are seen to dip X. 50° E.. at an angle of 25°. The facts above 



