100 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



succession of sedimentaiy formations. At the northern end of the sec- 

 tion the effect of the Sheep Momitain antichnal (A) has been indicated. 



Section IV rnns south and north a short distance "west of Saint Mary's 

 Station. It cuts one of the okl granitic hills (a). Resting against this 

 the schists have been represented in diminished quantity. They do not 

 appear upon the surface. Carboniferous limestone (/ and g) are found 

 on a line toward the Sweetwater, dipping northward. Tertiarj^ strata 

 cover them for considerable distance. Passing down the steep northern 

 slope of these latter, we reach older sedimentary formations, and with 

 them the continuation of the anticlinal ux)heaval {A). The line of ele- 

 vation continued ti-om the Wind Elver Eange is marked in both sections 

 as -£/. It is obscure, but can occasionally be found. 



Section V is taken along a line a short distance east of Saint Mary's 

 ranch. The old granite {a) is ahnost entirely hidden by suijerincumbent 

 Tertiary beds (T). Eesting upon the Prozoic rocks the schists {h) have 

 been sketched as forming but a small deposit, while the younger gran- 

 ites (c) are advancing toward the south. We know of their existence in 

 that region as well as of the j)resence of the anticlinal fold {A) through 

 some small outcrops that were found. •^N'orth of the edge of the Sweet- 

 water plateau (P) we find the sedimentary strata undisturbed. 



Section VI runs along a line about 2 miles west of the first granitic hills 

 north of the Sweetwater. From the south everything is obscured by 

 Tertiary deposits. At the river we observe the appearance of both 

 Silurian and Carboniferous strata. I hold the view that this is produced 

 by the effect of the anticlinal axis (A), which here coincides with the 

 axis of main elevation {U). In this section we pass the region of mini- 

 mum elevation of the oldest granite. To the northward the Prozoic 

 granites are indicated as reaching nearly to the surface, while the younger 

 granite extends still farther south. jSTear the northern end of the sec- 

 tion, the effect of the second anticlinal [B), which has been mentioned 

 in Chapter I, is introduced. 



Section VII cuts along a line about 13 miles west of Sweetwater Gap. 

 We there observe the reverse of what was seen in section IV. From 

 the south the Tertiary bluffs ( T) extend high up, obscuring everything. 

 North of those we find a series of sedimentary formations dipping to 

 the southward at very high angles. A narrow line of metamorphic 

 granite (c) runs along the outcrop of Potsdam sandstone {d). North of 

 this granite the Sweetwater Group covers the entire region to the base 

 of the Granite Hills. Underlying these the older sedimentary forma- 

 tions have been represented. Travelling eastward from that line we 

 find that the sedimentary beds rapidly disai)pear, but that the granite, 

 takes a turn to the southeast, and rises to a considerable elevation. It 

 there forms the main bulk of the Sweetwater Hills. Both the north and 

 south slopes are entirely obscured by Tertiary strata, so that nothing 

 further of the structure can be seen. I ascribe this rise to the effect of 

 the anticlinal uplieaval (A) which has continued in its general direction 

 until it reached this point. The southerly portion of the strata, having 

 been pushed high up, still remains, while their northern continuations 

 either never reached the same elevation, or were eroded and are now 

 covered by Tertiary beds. 



The granite continues to Elkhorn Gap, and from there eastward forms 

 the central iDortion of the hills to Whisky Gap. Section VIII, taken a 

 short distance east of the former, shows the main granitic mass occuijy- 

 ing the points. Another granitic outcrop (c) corresponds with that 

 faxther west in its action upon the strata of sedimentary formations. So 

 far as could be determined, these originally sloped from the northward, 



