BED-BOCK: SOUTH OF THE MOKELUMNE RIVER. 



123 



by no means a region of important hydraulic mining operations. A large 

 part of Calaveras County above the Bear Mountains is covered by volcanic 

 materials, which in places come down within a few miles of the foot of that 

 range, although nowhere invading it. The Bear Mountains seem to have 

 acted as a barrier during the volcanic period; neither gravel nor lava are 

 found in this range, or in the Gopher Hills. The volcanic, however, in the 

 central belt of Calaveras, on the line between Angel's Camp and San An- 

 dreas, occurs in patches, covering only the higher portions of the country ; the 

 bed-rock is well exposed in the lower regions, and especially in the valleys 

 of the rivers. 



In the vicinity of Mokelumne Hill the slates are very quartzosc and mica- 

 ceous. Their dip varies much more than their strike. At French Hill, one 

 fourth of a mile from Mokelumne Hill, the strike of the mica slates is N. 



67° W., and their dip 45° to the north-northeast. In Burns's Gulch, on the 

 opposite side of the Mokelumne River, the strike is nearly the same as in the 

 last-mentioned locality; the dip is a little higher, namely, 65°. There is also 

 a large amount of hornblende rock, or amphibolite, in this region. This rock, 

 which is made up of hornblende, associated with a little quartz and mica, is 

 of dark-greenish color, and is occasionally traversed by veins of epidote, with 

 which are associated masses of crystallized brown garnet. 



The slates in the vicinity of Angel's Camp are gray or light-green in color, 

 and fine grained. Near the Great Quartz Vein they become porphyrinic. 

 The bed-rock all along the line of outcrop of this vein is very similar in char- 

 acter to that described as occurring in similar relations in Tuolumne County. 



The most interesting feature of the bed-rock geology in Calaveras County 

 is the great development and peculiar character of the surface of the lime- 

 stone belt, the occurrence of which farther north has already been noticed. 

 This belt of rock is continuous from Kincaid Flat, a little east of Sullivan's 

 Creek, in Tuolumne County, as far as the Stanislaus River, and its average 



course is nearly uniform, although its width and the space it occupies on the 

 surface are quite variable. At Kincaid Flat its development hardly exceeds 

 a few hundred feet in width, but beyond Sonora it expands rapidly, and just 

 before reaching Springfield a line drawn across it at right angles to its trend 

 would be fully a mile in length. Just beyond Springfield its northeastern 

 boundary bends sharply around at a right angle, and runs for nearly two 

 miles towards the northeast, then turns again as sharply, at Shanghai Moun- 

 tain, and assumes its ordinary course of northwest. By this change of trend 



