12 



University of California Publications. 



[Geology 



are revealed as a result of the canon cutting by the West Walker. 

 These beds appear to be horizontal, and it is difficult to say 

 whether they are Quaternary or Upper Tertiary. A few large 

 bones have been found on their surface, and, as a matter of 

 record, it may be here stated that a few large bones have been 

 reported as found in building a road grade in the Wassuck 

 Range, southeast of these beds, and also that fish impressions 

 occur at the mouth of the canon just mentioned as cut by the 

 West Walker. 



Relative Age and Unconformity of the Igneous Bocks. — The 

 unconformity between the Bedrock Complex and the Super- 

 jacent Series is also well brought out by the stratigraphic rela- 

 tions of the igneous rocks of the two groups. The granites and 

 granite-porphyries of the Bedrock Complex appear to be intruded 

 into the Triassic, and cutting these are dykes of porphyrite, 

 which is perhaps also of the complex. The hornblende andesite 

 reposes in tilted attitudes upon the tilted abraded surface of the 

 Bedrock Complex. This was followed by the rhyolite, which is 

 found intrusive in the andesite in the form of tongues. Both 

 the hornblende andesite and the rhyolite yielded pebbles to the 

 shore drift of the Tertiary lakes which succeeded the extravasa- 

 tion of the rhyolite. But the andesite is not so abundantly rep- 

 resented as the rhyolite. The next lavas in order of occurrence 

 are the later andesite and the basalt. These two lavas appar- 

 ently succeeded the lacustral epoch, since they yielded no peb- 

 bles to the Tertiary Lake beds. The later andesite and the basalt 

 approximate horizontality. They both occupy eminences and may 

 be regarded as caps. The basalt occurs in many isolated and 

 detached areas, and these all, with the exception of that on the 

 Wassuck Range, are of the same altitude as the later andesite 

 cap. 



STRUCTURE. 



The Bedrock Complex. — The Triassic limestones are much 

 crumpled, folded and broken, and the accompanying batholithic 

 intrusions of granite and porphyries are also much fractured 

 and broken. The bedding planes of the shale are not exposed. 

 The axis of folding is nearly north and south, and there are indi- 

 cations, at least, that this structure would not be apparent in 



