28 



University of California Publications. 



[Geology 



The Schists. — Nos. 168a and 1686 ai*e samples of the schists 

 shown on Smg-ats'-e Ridge near the southern end, as may be 

 seen on the map PL 1. The grain of the schist is variable and 

 the slides differ but a little. Biotite and quartz, and occasionally 

 some small areas of sericitized feldspar may be seen through 

 them. Slide 168c is from the schistoid dyke which is contained 

 within this area, and which was mentioned as containing dissemi- 

 nated sulphides of iron and copper. It differs not essentially 

 from the other two. In slide 1686 the biotite is somewhat decom- 

 posed to epidote and chlorite near the feldspathic areas within 

 the slide. 



SEQUENCE OP THE IGNEOUS ROCKS. 



The relative ages of the igneous rocks are granite, granite- 

 porphyry, porphyrite, hornblende andesite, rhyolite, later ande- 

 site, and basalt, the relation of the last two not being determined. 



Of the lavas, two were traced to points of exit and two were 

 not. The hornblende andesite and the rhyolite were found in 

 dykes as well as distributed on the surface, but the basaltic and 

 later anedsitie rocks were not found in any sort of vent. This 

 does not signify, however, that their points of exit are greatly 

 distant, but perhaps that the writer's acquaintance with them 

 is less. 



THE ORE DEPOSITS. 



The deposits of value carry copper and gold, but the two 

 metals are not associated with one another in pay values. The 

 richest copper deposits carry no gold, except perhaps as a trace, 

 though occasionally a gold bearing vein contains copper, but 

 not in values sufficient to warrant treating the ore for that metal 

 alone. 



Geology of the Deposits. — It has been stated in considering 

 the general geology of the region that the mineral veins are con- 

 formable to either one or the other of the main structural features 

 of the region, and such being the case, it would seem that they 

 were consequent upon the inauguration of these systems, but it is 

 not to be inferred that they were formed subsequently to all the 

 structural features. In fact, there seems to be very positive evi- 

 dence that they preceded the present topography, which stands as 

 a record of the later stages of deformation. In some instances 



