st. JOHx.] MT. LEIDY HIGHLANDS. 459 



sandy marls, clays, sandstones, and occasional limestone layers, includ- 

 ing - near the middle several layers of impure lignite. Arenaceous ma- 

 terial predominates, and the lower hundred feet has a gray ashy color. 



Overlooking a large part of the southern slope of the Mount Leidy 

 highlands, from Station XL VI on the south side of the Gros Ventre 

 Valley, it is found to he traversed by three parallel belts, which comprise 

 so many rather conspicuous lithological zones parallel to the longer axis 

 of the highlands. The first belt or zone is composed of the deep-red 

 arenaceous deposits, banded with paler-colored layers, characteristic of 

 the "red beds" or Triassic. These deposits present their edges to view 

 in a line of beautifully-eroded bluffs on the north side of the Gros Ven- 

 tre, the strata dipping gently northward. Beyond the "red beds," 

 north, the slope is broken by long, low ridges, in the southern face of 

 which light-drab deposits appear, composed apparently of shales and 

 arenaceous beds, with perhaps calcareous indurated bands, and a heaver 

 mass of brown-drab firmer material above, reaching a thickness of sev- 

 eral hundred feet. The latter deposits form a belt at the foot of the 

 steeper ascent culminating in Mount Leidy, and stretching to the south- 

 east, or east-southeast, where they occur in quite prominent ridges, cut 

 across by a tributary which rises in the hills beyond. Farther on in the 

 same direction they do not appear so strongly marked, and soon pass 

 from view behind a near shoulder on the northern flank of the Gros 

 Ventre Eange. These beds seem to dip gently to the northeast, the line 

 of peculiarly regular escarped ridges in which they outcrop gradually 

 rising to the northwestward, where, however, as in the opposite direc- 

 tion, they soon cease to form so prominent and well-defined topographic 

 and geological features as seen at this distance. 



In the intervening nearer slope such exposures of the component strata 

 as appear seem to indicate a more disturbed belt, in which the beds are 

 sharply folded along a line apparently parallel with the general trend 

 of the Gros Ventre uplift. More than this was not clearly indicated. 

 These deposits are doubtless the same as those described by Dr. Hay- 

 den in the immediate vicinity of the Gros Ventre. The disturbed or 

 folded belt may include the later Mesozoic formations, but the higher 

 and wider belt is probably wholly composed of Tertiary deposits, in- 

 cluding the superior lignitic series of the region. 



To the north of the drab belt the hills are less regular in outline, are 

 more eroded into sharp, buttressed ridges and deep gullies, dotted with 

 trees and patches of undergrowth. These hills appear to be composed 

 entirely of the brownish ash-colored deposits above and lighter ash or 

 drab beds with comparatively thin beds of yellowish-buff sandstone be- 

 low. They form a heavy deposit a thousand feet or more in thickness 

 in the cluster of hills around Mount Leidy. So far as could be deter- 

 mined, these strata uniformly incline at a moderate angle northwards, 

 and such undoubtedly appears to be their dip in the northern slope of 

 the highlands. 



The foot-lolls along the western side of this highland region are cov- 

 ered with a fine brown soil, with scarcely any coarse material visible in 

 their surfaces ; their higher slopes generally covered with pine forests 

 and undergrowth. A few miles north of the Gros Ventre the foot-hills 

 terminate more abruptly on the terraced plain of the basin. Obscure 

 exposures of light or white fragmentary limestone were here met with, 

 which, from the similarity in color and texture, was taken to be identical 

 with the thin-bedded limestone occurring in the late Tertiary deposits 

 in the vicinity of Station XLV. Similiar patches of limestone debris 



