ffi. jomf.] 



AECH^AN AREAS. 475 



in a conical peak overlooking tke great western foreland, in the vicinity 

 of the sources of North Fork of PiciTc's Eiver and Leigh's Creek, the 

 upraised volcanics of the foreland here, as to the south, coming into 

 d&ect contact with the Archnean rocks. But to the north of this great 

 spur the watershed crest is soon capped by the Siliu-ian, the Archaean 

 being crowded to the eastern border and finally abruptly terminates in 

 a comparatively narrow, low ridge, beyond which spreads the high 

 volcanic plateau separating the Henry's Fork drainage from the lake 

 region. This northern terminal ridge, like Mount Moran, hes to the 

 east of the water-divide of the range, and its northeast flank Professor 

 Bradley found partially enveloped in a remnant of Palceozoic deposits. 

 But south of Jackson's Lake, to the vicinity of the canon of Fighting 

 Bear Creek, the whole eastern face of the range shows the bared 

 ArchJEan ledges in one of the most majestic mountain fronts on the con- 

 tinent. South of the latter point the heights are crowned by the sedi- 

 mentaries, which gTadually increase by the addition of successive for- 

 mations in the order of their superposition as the Archaean nucleus de- 

 clines in elevation, until, at the southern extremity of the range, the 

 sedimentaries lap continuously over the mountain ridge in a series of 

 folds whose continuity iu the direction of their longitudinal axis seems 

 to have been broken by the mountain corrugations in the Snake Eiver 

 Eange, which intersect the Teton uplift at a sharp angle. 



Along the summit of the range to the south of West T^ton Creek the 

 Archaean rocks at first occur in a narrow belt, with ganglion-like ex- 

 pansions or isolated areas in the beds of the amphitheatres in which the 

 main west- side drainage is gathered before it flows out into the basin 

 through the gorges the streams have cut across the sedimentary fore- 

 land. This southern extension of the Archaean also appears to be largely 

 composed of gneissose and schistose rocks, the structural features of 

 which, however, are too indistinct to be readily made out except by 

 numerous and careful examination, for which imrpose our time was far 

 too hmited. 



The stupendous elevatory movements in which originated the range, 

 resulted iu a vertical displacement of probably not less than 15,000 feet. 

 It appears to have been a long eUiptical zone, along the eastern border 

 of which the forces were concentrated, resulting iu the tnting of the 

 mountain mass with abrupt dips on the east and more moderate inchna- 

 tion on the west ; while in the central portion, in the vicinity of the 

 present dominating heights, it is almost impossible to believe otherwise 

 than thattheupthrustof the granitic core completely severed the sedimen- 

 tary and metamorphic crystalline mantle. Along the greater extent of 

 the eastern front the displacement was probably abrupt, and if it did 

 not result in the faulting of the sedimentary deposits, it so fractured 

 them as to give easy access to those potent agents in mountain degrada- 

 tion resident in the atmosphere, and which have left but the meagre 

 skeleton of the foundation of this side of the range, from which we may 

 endeavor, Avith greater or less success, to conceive the mighty changes 

 that have been wrought in the lines of its contour, and rehabilitate the 

 mountain to its prime. 



The Gros Ventre Eange shows a less lofty and more uneven Archaean 

 belt, the rocks at the western end consisting chiefly of much distorted 

 gneissic and schistose ledges. As in the T(5ton Eange the disturbances to 

 which these early metamorphic rocks were subjected prior to their up-' 

 heaval in the present mountain range, the few facts we possess throw 

 little light on even the general phases of these early movements ; but in 

 the later upheaval the records, as laid open to inspection by erosive 



