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University of California Publications. [Geology 



their highest altitude, and from this on the ridge, which is now 

 still higher, is continued by granite and metamorphics, the rhyo- 

 lite being relegated to the flanks of the ridge. The andesite is 

 rarely to be seen from this on southward, and only then as a few 

 loose blocks here and there, separated by dividing summits from 

 that which is in place. Part of the stock from which it may 

 have been derived may be covered by seolian sands or debris; 

 or else these erratics are the remnants of a once extensive flow. 

 The rhyolite near the southern dyke is frequently faulted, both 

 transversely and lengthwise of the ridge, so that it is much 

 broken. The contact which we now come to is that between the 

 rhyolite and the granite. It appears to be not a fault contact 

 from the evidence the writer was able to obtain. There was no 

 contact metamorphism noticed, nor was there found any inclu- 

 sion of the granite in the rhyolite. A small area of conglomerate 

 is revealed near the contact where erosion lias carved away the 

 rhyolite. No bedding is shown, and every pebble, almost without 

 exception, is faulted. The formation is not shown on the map 

 PI. 1, the area being too small. The rhyolite of this ridge appears 

 not to present the structure which, according to the terminology 

 of some writers, would be designated as sheeted. The andesite 

 near by possesses this structure in a marked degree. At this 

 contact the rhyolite ceases to be prominent in the ridge, and the 

 hornblende andesite does not continue farther southward. The 

 rocks that are now encountered are granite and granite-por- 

 phyry, schists, garnetiferous rocks, basalt and limestone. The 

 contact between the granite and granite-porphyry is more irreg- 

 ular than it was possible to show on the map. The contact 

 between the granite and the schists and garnet rocks is also irreg- 

 ular. The strike of the granite-porphyry is east and west, and 

 it occurs as a very wide intrusive in the granite. The strike of 

 the belt of schists is somewhat north of east. The belt of schists 

 contains numerous segregations of copper ore, and a reef of 

 exceptional interest, containing disseminated sulphides of copper 

 and iron. It appears to be a metamophosed dyke. In places 

 it has included in it a light colored rock, which may be pieces 

 of the granite that were caught up at the time the dyke was filled. 

 More will be said of this supposed dyke under the head of ore 



