354 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



and if we succeed in ascertaining the actual stratigrapMc sequence of 

 the geological series, mucli will have been secured of value as well to 

 the i^alaeontologist as to the geologist. 



A couple of miles to the southwest of Station XV, in the Ioav grassy 

 slopes on the west side of the little basin, a narrow ledge of soft, thin- 

 bedded, gray sandstone outcrops in a miniature liogback ridge, dipping 

 steeply to the south westward, or 54P, S. 40° W. This ledge undoubtedly 

 belongs to the same series shown in Station XVI section, and forms the 

 outflanking exposure on this side of the WiUow Creek hills. But de- 

 scending, east, to the West Fork of John Gray's Creek, whose valley is 

 flooded mth basalt, and crossing over to the lower ridge embraced be- 

 tween the West and East Forks, the same series of deposits is again 

 encountered, where the strata are bulged up and finally severed by the 

 extrusion of igneous matter which forms the culmination of the ridge. 



This ridge extends from the northwest in a southeasterly direction, 

 about six miles, and j)arallel with the higher ridge described in a pre- 

 ceding page, from which it is distant only about four miles. A little 

 south of the middle it is surmounted by a wedge-shaped comb of rock 

 composed of a handsome variety of hornblendic trachyte, the crest of 

 which was selected for Station XVII, and which attains an altitude of 

 about 7,200 feet. The south end of the crest descends sharply to the 

 broken continuation of the ridge, while to the northwest it more gently 

 slopes, in places occupied by the sedimentaries, again by the narrowing 

 volcanic mass, which latter finally disappears, the sedimentary beds lap- 

 ping without Ibreak in their continuity over the ridge. A section across 

 the ridge along a northeast and southwest line, perhaps half a mile north 

 of Station XVII, commencing with the northeasternmost exposures, ap- 

 pearing in the gentle slopes that reach down into the basin-like valley 

 of the East Fork of John Gray's Creek, just above the point where it 

 begins its caiioned course in the basalt, is given below : 



Section across Station XVII ridge. 



1. Fine reddish-stained soil, appearing in the low upland terrace 

 bordering the level creek bottom. It indicates subjacent shaly deposits. 



2. Eed shales and included sandstone layers, obscurely exj)08ed in 

 the grassy slopes. 



3. Heavy bed of reddish-gray, even-bedded sandstone, weathering 

 into flags ; dip northerly. 



4. Buff, reddish-tinted, thin-bedded, rather firm sandstone; some- 

 -times a semi-quartzite with slickenside surfaces, including shaly gray 

 sandstone, and underlaid by heavy-bedded, reddish buff sandstone, dip- 

 j)ing 35° to 45°, east of north. The ledge forms a low hogback, sev- 

 eral yards across, and which may be traced to a distance in the decliv- 

 ity. The ui)per ledge contains obscure vegetable impressions, fragments 

 of limbs, ancl algse-like markings. The surfaces of certain layers are 

 -undulated by large ripple-markings. 



5. To the southwest of the last-mentioned bed, 60 or 70 yards, a low 

 parallel comb of soft, thin-bedded, gray sandstone breaks the surface, 

 the bed showing a thickness of 5 to 10 feet, and dipping 45° to 50°, N. 

 ,25° to 30° E. 



6. Eed shales, obscure exposure. 



7. In the slope of the main ridge about 300 yards distant from bed 4, 

 occurs an obscure outcrop of drab,' brittle, earthy limestone, containing 

 numerous small gasteropods, a few medium-sized lamellibranchs, and a 

 ■minute fish-tooth. 



