330 REPORT UNITED STATES GEOLOGICAL SURVEY. 



and sweeping* down in that direction so as to cover that side of the ele- 

 vation. 



At the foot of the southeastern spur a heavy bed of light-colored, 

 rough- weathered quartzite appears, dipping 25°, east 30° south ; the same 

 deposit again outcropping in the south side of the little gorge which 

 cuts across the ridge just south of Station II. Besting on the latter 

 bed occurs an obscure exposure of rough- weathered buff-gray siliceous 

 limestone, containing a few poorly-preserved fossils, crinoidal columns, 

 and an undetermined brachiopod shell, which may be a Hemipronites. The 

 latter rock appears in a low shoulder at the southeast foot of Station II 

 hill, to the east of which the rocks are again hidden beneath the soil. 



From Station II the ridge rapidly trends round into the northeast, 

 showing several low rugged summits. In one of these points, a mile or 

 so to the northeast of Station II, obscure outcrops of limestone debris 

 were crossed, which areapparently identical with the conglomeritic lime- 

 stone exposures above mentioned underlying the Zaphrentis limestone 

 ledges which appear in the north bank of Boss Fork. A little farther 

 on to the eastward, indeed, a heavy mass of overlying dark-gray Car- 

 boniferous limestone offers the same association and succession of beds 

 as noted at the above-mentioned locality some four or five miles to the 

 south. In an accompanying plate will be found a generalized section 

 exhibiting the stratigraphy and structural features of the monoclinal 

 ridge forming the northern extension of the Putnam ridge within this 

 district. 



HIGHAM'S PEAK -SEDGE, OR ROSS PORK — LINCOLN AND BLACKFOOT 



DIVIDE. 



Extending northward from our south line is a low ridge, which may 

 be designated as the Higham's Peak Bidge, after the peak which con- 

 stitutes the dominating topographical feature. For the most part this 

 belt forms a broad low divide between the highland course of the Black- 

 foot on the east and the depression which intervenes between this and 

 the Mount Putnam ridge on the west. The northern portion of this 

 depression is occupied by the Lincoln Valley, while the southern half 

 belongs to the highland basin of Boss Fork. This latter basin and the 

 low divide which separates it from the head of Lincoln Valley or Four- 

 Mile Creek, as it is locally known, embraces an elliptical area of undu- 

 lating grassy surface in the main mantled with detrital materials, with 

 evidence here and there of the fine brown soil which is common if not 

 peculiar to the disintegration of the Pliocene volcanic deposits. But as 

 to the existence of the latter deposits in this basin, further evidence was 

 not observed. 



Lincoln Valley is excavated out of Triassic and Jurassic beds, while 

 that portion of the divide still to the north is flanked by a broad terrace 

 which gently descends to the westward and terminates in low bluff ele- 

 vations which here define the Snake plain. This border terrace has 

 much the same character as the above-mentioned outlying Pliocene 

 areas, but its mantle of soil completely conceals the nature of the deposits 

 of which it is composed. As in the forks of Boss Fork, the basaltic lava 

 is again met with in the debouchure of a small stream heading in 

 Higham's Peak, and thence northward these deposits increase in fre- 

 quency of occurrence until they assume the entire area in the vicinity of 

 the debouchure of the Blackfoot Biver, from whence they curve round 

 to the southward, apparently flanking the eastern slope of this highland 

 belt to a point near the south line of the district. 



