232 IRVING. 



of Green mountain, and a large mass of that rock occurs on the 

 saddle between Green and Bald mountains. 



On the slopes of Terry peak, in Nevada and Fantail gulches, 

 and throughout the entire district known as Ruby Basin, sheets 

 of igneous rock occur in great abundance. In the Cambrian 

 west of Englewood there is an enormous mass of fine-grained 

 phonolite of a brilliant green color, which is apparently present 

 in the form of a very large sheet. Another sheet of biotite- 

 phonolite appears southeast of Aztec and covers an extensive 

 area. On the railroad from Aztec to Englewood many sheets 

 of phonolite are seen, and also sheets of a white, exceedingly 

 fine-gramed rhyolite, which is intersected by a dark-colored 

 quartz-porphyry in very small dikes. 



3. Dikes in the Cambrian. 



Besides the sheets and laccolites, dikes appear in considerable 

 numbers in the Cambrian. In the Ruby Basin district vertical 

 dikes of quartz-porphyry occur. Some of them are of consid- 

 erable size, as that which juts out from Terry Station into the 

 head of Fantail gulch. Others are very small. 



Phonolite also occurs in dikes throughout the region and 

 when found in contact with the quartz-porphyry always inter- 

 sects the latter, a relation which proves the phonolites to be the 

 relatively later intrusives. Instances are the long, coarse tin- 

 guaite dike near the Rua mine, the dike with east and west 

 strike in Squaw creek below the Gushurst mine, the dike north- 

 west of Twin Peaks and many others. 



C. Intrusions in the Carboniferous. 



These are comparatively few in number and of limited areal 

 extent. They cannot be classed as dikes, sheets or laccolites, 

 but are more in the nature of thick irregular masses, which 

 seem to belong to none or to all three of these types. The 

 most conspicuous is Elk mountain. 



Elk i/ioi/nlaiii. — This hill is situated on the Carboniferous 

 plateau, something less than one mile, directly east of Crown 



