170 GEOLOGICAL SURVEY OF THE TERRITORIES. 



and porphyritic. Its specific gravity is 2.39. On reaching tlie top of 

 the canon we encamped in Pleasant Valley, a beautiful little valley set 

 in the mountains like a gem. Its elevation is 6,086 feet. Near our 

 camp was a deep, narrow gorge cut through rock, which, on examina- 

 tioD, proved to be a true porphyritic phonolite, having disseminated 

 through it crystals of sanidine,. nepheline, and hallynite. The rock is 

 of a dark-gray color, very compact, having a specific gravity of 2.75 ; 

 the crystals occurring in spots, occupying about a quarter of an inch 

 each, and from one to two inches apart. The haiiynite occurs as red- 

 dish, octagonal crystals. The nepheline is the variety sommite, and is 

 in small grains ; while the sauidine, or orthoclase, is in tabular crys- 

 tals. I insert here the mineralogical composition of some phonolites 

 of Bohemia, given by G. Jenzsch : 



Per cent. 



Sanidine, estimated at 53. 55 



Nepheline, estimated at 31. 76 



Hornblende, (arvendsonite) 9. 34 



Titanite 3. 67 



Pyrites 0. 04 



I shall take the earliest opportunity of making a chemical analysis of 

 this rock. The occurrence of these phonolites would go far toward 

 proving the age of the eruption, even though we had not the Tertiary 

 formations beneath it, for no true phonolite has been found to be of 

 other than Tertiary or still more recent origin. The following day we 

 continued on our way across the mountains, passing over the divide, 

 the elevation of which was 7,044 feet. The more modern rocks were 

 conglomerates, presenting little or no interest. I obtained some speci- 

 mens of trachyte, which are vesicular, of a white color, having a reddish 

 tinge in some parts. I also obtained specimens of a vesicular rock, 

 which I consider to be a phonolite, although I had not the opportunity 

 of observing it in position. One of the specimens was of a dark-gniy 

 color, having a specific gravity of 2.57. The specific gravity of the light 

 varieties was 2.3. After crossing the divide our way lay over Pliocene 

 formations, in which I obtained a white sandstone comjwsed of very 

 fine pebbles, cemented by a calcareous matrix. The older rocks were 

 limestone conglomerates, upon which rested white and red sandstones. 



The 30th of June we spent in camp, visiting a peak near us where we 

 found the limestone conglomerates at the base with sandstones on 

 top. The next day our route was through a rolling country, now pass- 

 ing over a hill and now through the valley of a small stream. I procured 

 specimens of a very compact, dark phonolite, having a specific gravity 

 of 2.4. The recent rocks were of Pliocene origin. Some of them consist 

 of very snmll, bluish, siliceous i^ebblesin a white, siliceous matrix. Upon 

 these were grayish calcareous sandstones, also Pliocene. They consist 

 of minute red and black pebbles cemented by lime. On top of these 

 were yellowish calcareous marls. We camped at night at an elevation 

 of 6,988 feet, in tlie midst of gneissic hills, which become granitoid in 

 places. The following morning we entered Wild Cat Canon, a pictur- 

 esque, gorge-like valley, the rocks of which stand out boldly on either 

 side. At the head of the canon I found a vein of coarse granite, con- 

 taining labradorite in good cleavable masses. In some of the specimens 

 the play of colors was particularly fine. There were also some good 

 crystals of black mica, (biotite.) The surrounding rocks Avere tine- 

 gramed granites of a reddish hue. On top of the granites were 



