UNCONFOUMITV. 297 



sented by tlie contact. In tliat case, however, still greater irregularities 

 in the line of contact would almost certainly exist, as well as outlying 

 Datches of nietaniorphic rock and tr;uisiti(Mis b'.itween metanior[)hosed and 

 unaltered beds along the contact. The presence of siliceous and serpentinoid 

 pebbles in the Cliico conglomerate would also be very m}-sterious. Tlio 

 non-conformity above the metauiorpliio series is thus substantially certain 

 from the obser\-ations at New Idria alone. Confirmatory evidence was ob- 

 tained on the north fork of Cantua Creek, some five miles southeast of New 

 Idria. At that locality the creek cuts through hills capped with heavy beds 

 of Chico sandstone, which are inclined at an angle of approximately 30° 

 and strike at right angles to the course of the creek; but this interval is 

 only a few hundred feet in width and there can hardly be a doubt that, if 

 the talus were removed, the Chico beds would be found resting on the up- 

 turned edges of the metamorphic rocks Had the thin-bedded rocks been 

 driven into their present position after the deposition of the Chico rocks, 

 the latter could not, in my opinion, have been so little disturbed. The beds 

 are not visibly flexed and form cliffs at their upper end. In the creek the 

 metamorphic, thin-bedded sandstones are exposed in a nearly vertical posi- 

 tion. The interval between the creek bed and the exposed sandstones is 

 covered by detritus and vegetation. 



The mine affords one important exposure of the contact below the 

 Chico. This is in the Bell tunnel, the position and course of which are shown 

 on the map. Its month is in the Chico strata, and it passes far into the meta- 

 morphic mass. Th3 rocks near the entrance are tliick beds of soft, tawny 

 sandstones, with occasionally thin masses of shale. They are unbroken and 

 dip north 30^ east at angles of 65°, with some small variations. As the 

 contact is approached breaks begin to appear in the sandstones, due to spe- 

 cial disturbances in the region of the mine, which will be referred to in de- 

 scribing the deposit. While there are fractures and small fliults along this 

 part of the tunnel, the rock nowhere seems to be flexed and the beds re- 

 cover their normal position at frequent intervals. The beds are neither silicl- 

 fied nor serpentinized, but, as at the surface, there are occasional stringers 

 of calcite and gypsum. At a point 90 feet northward from the last station 

 before the main cross-cut is reached, or at a distance of al.)Out twenty- 



