REGION OF THE OARLIN PEAKS. 589 



The eastern of the CarHn Peaks is a high, flat, table-shaped mountain, 

 made up of the typical red porphyritic rhyolite. The same character of 

 rocks extends to the west of the upper part of Annie Creek, and covers the 

 western slopes of the range where the Emigrant Road crosses it. Under 

 it, near the river, is exposed an outlying portion of the trachyte body, and 

 here the rhyolite itself very closely resembles the trachyte, but is distin- 

 guished from it by its containing a considerable amount of free quartz. 

 With its prevailing sanidin-feldspar, it has also some finely- striated triclinic 

 feldspars and black hornblende, but no mica, in a reddish-brown micro- 

 felsitic groundmass. 



The rhyolites which form the eastern slopes of the range north of 

 Palisade Canon, in the neighborhood of the Emigrant Road, are grayish-red 

 rocks, containing almost no macroscopical crystals, with the exception of a 

 few sanidin and plagioclase-feldspars. The microscope discloses no quartz, 

 but shows that the groundmass has a sphserulitic structure showing a radial 

 fibration. The numerous cavities are seen to be lined by a light-gray crust, 

 made up of fine layers of different-colored hyalitic opaline material. 



