ST. joira.] TIPTON RANGE. 415 



t-ory of tliis spur and some 8 miles south, or 13 miles south of Station 

 XXXII, in a high ridge on which Station XXXV was located, the sedi- 

 mentaries again appear high \\\) on the western flank of the range, defin- 

 ing the southern limits of the Archaian area, and breaking down into a 

 magnificent amphitheatre based upon the rapidly rising metamoriihic 

 floor which culminates in the great axial ridge along the eastern bor- 

 der of the range. The section here revealed is reproduced in section 

 C. It shows a great foreland rising up from the level of Pierre's Basin 

 with gradually steepening acclivity, its foot bathed in the volcanics, 

 porphyritic trachytes, to an elevation of 800 feet above the edge of the 

 basin and terminating in successive lines of clitt's and steep taluses of 

 debris facing the east. The ascent is over grayish-blue, spar-seamed, 

 cliertv limestone, containing abiindance of characteristic Carboniferous 

 fossils, the strata inclined at angles of 10° to 20°, W. 25° to 35" X. 

 The descent of the slope is in places so much more considerable than 

 the inclination of the strata that the latter are often carved into great 

 bosses, or gently tilted tables, surmounting the western mountain flank. 



It is very difficult, if not impossible, to obtain a perfect section of these 

 Carboniferous deposits. Even in the abrupt east face, in which the ledges 

 show thin edges, the exposm^e consists of mural walls of limestone, 

 separated by steep debris slopes, arranged in alternating order to a depth 

 which probably includes a thickness of 800 feet of strata overlying the 

 heavy-bedded buff magnesiau limes tones of the Niagara epoch. AVhether 

 these debris slopes indicate the position of clay and shaly layers, or the 

 mural ledges only show firmer limestone beds, alternating with more 

 fragmentary and easily degraded strata, was not ascertained ; it is, how- 

 ever, probably attributable to both conditions, the more compact beds al- 

 ternating with both clay and fragmentary limestone deposits. Eising to 

 view from beneath the Carboniferous, the Xiagara buff magnesiau lime- 

 stone extends eastward into the Alpine basin like a gigantic pier, often re- 

 vealing in mural exposures 200 to 300 feet, the base of the cliffs buried in 

 ledge, which is easily recognized by its uniform escarpments, and the 

 debris which conceals the total thickness of the formation. This great 

 castellated forms into which its crest weathers, is in turn succeeded by 

 the thinner-bedded, rough, dark drab limestones of the Quebec Group, 

 which rest upon rusty reddish quartzites liartially flooring the amphi- 

 theatres. Of the Quebec limestones there is seen a thickness of perhaps 

 300 to 400 feet, the underlying sandstones and quartzites showing about 

 200 feet more. 



Looking northward from Station XXXV, the sedimentaries soon cease, 

 and with them the extreme ruggedness of the smface, which is moidded 

 in the Arclipean, which sweeps up in gTand, massive ridges, in which the 

 streams have worn comj)aratively shallow channels. While there is 

 unmistakable evidence here of an excess of upheaval of the Archaean 

 nucleus of the range, by which the sedimentaries were crowded farther 

 to the westward in the region intervening between Leigh's Creek and 

 the North Fork of Pierre's Kiver, the present surface contours are due 

 to the extensive denudation to which this part of the range has been 

 subjected antecedent to the flow of volcanic matter which here rests on 

 the metamorphics, and which has also undergone extensive erosion within 

 comparatively modern times. The volcanics, represented by the ancient 

 porphyritic trachytes which appear in rough, vesicular, nisty ledges 

 and light drab and pink trachytic beds, are traced in more or less well 

 defined benches, which reach an actual altitude of 7,400 feet between 

 Bear Creek and West Teton Eiver, where they gently incline toward the 

 basin. In the debouchure of the latter stream these deposits have been 



