KAMMA MOUNTAINS. 789 



wliicli occur in great variety, and give most brilliantly variegated colors to 

 the liill slopes. Although presenting such great variety of" color in the 

 field, they present no great variety of mineralogical composition, being 

 generally poor in crystalline ingredients. The breccias and earthy varieties 

 predominate, and in color range from a white at the base of the hills, through 

 delicate mauve and bright red, into yellow at the summit. A white rhyo- 

 lite, in the dry water-course between these hills and the middle group, pre- 

 sents a finely banded structure in wavy lines, and abounds in small druses 

 lined with quartz crystals. Under the microscope, its groundmass is seen to 

 be neither microfelsitic nor distinctly crystalline, while the banded appear- 

 ance is due to the arrangement of the grains and fibres of imperfectly 

 crystallized material in the groundmass. The breccias, on the other hand, 

 present in the angular fragments which are enclosed in them a great variety 

 of micro-structure in the same rock. 



The lower spurs of these hills" are smooth and gently sloping, and cov- 

 ered with detrital material, so that little could be learned of their composi- 

 tion except that re-arranged rhyolitic material seems to predominate. A 

 dark-brown outcrop about half a mile north of Rabbit Hole Spring, for 

 instance, was found to be made up of fragments of various cherty rhyolites, 

 caiT3^ing free quartz, cemented by a sort of argillaceous material. 



Toward the desert, the Kamnia Mountains present long gentle slopes, 

 descending between 100 and 200 feet in the mile, in which, in places, notably 

 along the slopes of the western group, deeper gullies disclose the presence 

 of stratified beds of soft crumbly material, largely volcanic ash, which indi- 

 cate a Tertiary deposit. 



At the northern limit of the map is rej)resented the southern point of 

 a prominent range of mountains, which forms the eastern border of the 

 Black Rock Desert, and whose culminating point, known as Mount V^ry, 

 reaches a considerable altitude, probably between 8,000 and 9,000 feet. Of 

 the portion included within the limits of the map, the crest and eastern 

 slopes are formed of trachyte, a fine-grained rock, of reddish-purple color 

 and conclicidal fracture, in which no crystalline ingredients except minute 

 feldspar crystals are visible to the naked eye. The microscope discloses no 



