Eleventh annual report of the United States Geological and Geographical Survey of the Territories : embracing Idaho and Wyoming : being a report of progress of the exploration for the year 1877 . anite forms the coreupon which atmospheric erosion has wrought with so wonderful resultsin mountain architecture. As seen from the opposite side of JacksonsBasin, the mass in the great peak seems to have a bedded structure, withdips, according to Professor Bradley, but little from the vertical; butfrom the west the mountain presents vertical precipices of enormousheight, in which the granite appears i
Eleventh annual report of the United States Geological and Geographical Survey of the Territories : embracing Idaho and Wyoming : being a report of progress of the exploration for the year 1877 . anite forms the coreupon which atmospheric erosion has wrought with so wonderful resultsin mountain architecture. As seen from the opposite side of JacksonsBasin, the mass in the great peak seems to have a bedded structure, withdips, according to Professor Bradley, but little from the vertical; butfrom the west the mountain presents vertical precipices of enormousheight, in which the granite appears in huge angular blocks or slab-likemasses with j>ohshed, glistening surfaces. To the north the Archaeanarea expands, occupying quite the entire breadth of the range along aline drawn through Mount Moran, and over the greater part, if not thewhole, of this bared area the rocks are gneissic, or such their peculiarsharp, jagged manner of weathering pronounces them. Immense sur-faces of the rocks in this quarter are laid bare by erosion, in whichformer glaciers may well be credited with an ample share. The crest ofthis expanded belt forms a iprominent spur which abruptly terminates A 5 ?a. «.johx.] ARCH^AN AREAS. 475 in a conical peak overlooking tlie great western foreland, in the vicinityof the sources of ETorth Fork of Pierres Eiver and Leighs Creek, theupraised volcanics of tlie foreland here, as to the south, coming intodirect contact with the Archaean rocks. But to the north of this greatspur the watershed crest is soon capped by the Silurian, the Archaeanbeing crowded to the eastern border and finally abruptly terminates ina comparatively narrow, low ridge, beyond which spreads the highvolcanic plateau separating the Henrys Fork drainage from the lakeregion. This northern terminal ridge, like Mount Moran, lies to theeast of the water-divide of the range, and its northeast flank ProfessorBradley found partially enveloped in a remnant of Palaeozoic south of Jac
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