8T.J0HX.] MT. LEIDY HIGHLANDS. 459 



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

 ing; near the middle several layers of imi)ure lignite. Arenaceous ma- 

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



Oveilooking- a large part of the southern sloi>e of the JNIount Leidy 

 higldands, from Station XL VI on the south iside of the Gros Ventre 

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

 so many rather conspicuous lithological zones ])arallel to the longer axis 

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

 arenaceous deposits, banded with paler-colored layers, chara(;teristic of 

 the "red beds" or Triassic. These dei)osits present their edges to view 

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

 tre, the strata di])ping- gently northward. Beyoiid the -'red beds," 

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

 w^hich light-drab deposits appear, composed apparently of shales and 

 arenaceous beds, with perhaps calcareous indvu^ated bands, and a heaver 

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

 eral hundred feet. The latter dei)osits 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 Avhich 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 Jiortheast, the line 

 of peculiarl}^ regular escarped ridges in which they outcrop gradually 

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

 tion, they soon cease to form so prominent and well-defined toi)ographic 

 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 tlie Gros Ventre uplift. More than this was not clearly indicated. 

 These deposits are doubtless the same as those described by I3r. 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 com]30sed of Tertiary deposits, in- 

 cluding tlie 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 yelloAvish-bulf sandstone be- 

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

 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-hills along the western side of this highland region are cov- 

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

 their surfaces ; their higher slopes generally covered with pine forests 

 and undergTOwth. 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 fi'agmeutary limestone Avere 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 



