KAMMA MOUNTAINS. 787 



unaided eye. Under the microscope, well-defined hornblende can be distinr 

 guished, associated with light-brown grains, which are probabl}' epidote, 

 while the fresh plagioclases are seen to contain hornblende dust, but no 

 quartz has been detected. 



In the desert, a mile or two beyond the western extremity of this ridge, 

 is an obscure outcrop of a very characteristic dolerite. It is a rather 

 fine-grained crystalline rock, of irregular fracture, and of a dark reddish- 

 brown color on the weathered surface, in which crystals of augite up to a 

 quarter of an inch in length and fine plagioclases can be distinguished. 

 White calcite is deposited in crevices in the rock, and in some cases forms 

 pellucid crystalline grains. The microscope detects also fine magnetite 

 grains and hexagonal laminae of specular iron, with a little olivine, while 

 between the feldspars and augites is a little dark globulitic base. This 

 dolerite is interesting on account of its rarity, the only other occurrence 

 in this region being a small hill at Black Rock, which will be described 

 later. 



At the eastern extremity of the ridge, in the gap of the dry water- 

 course already mentioned, is an outcrop of a rock that has been classed by 

 Zirkel as a trachyte, but which, in general physical character and appear- 

 ance, closely resembles the andesites, with which it is nearly connected. 

 The dacite color, which is here indicated by mistake on the map, belongs to 

 an outcrop found in the desert a little to the eastward. This latter is a fine- 

 grained rock, resembling in general appearance and structure a compact 

 sandstone, of gray color. The only constituents to be distinguished in it 

 by the naked eye are fine grains of limpid quartz. Under the microscope 

 can be seen, besides the plentiful quartz-grains, well-striated plagioclases 

 and altered hornblendes, in a groundmass of a somewhat rhyolitic nature. 

 The trachyte at the gap is a greenish-gray, rock, of moderately rough 

 texture, containing, in a homogeneous-looking groundmass, white decom- 

 posed crystals of sanidin-felspar, occasional dark -brown hornblendes, with 

 a few fresh plagioclases. The microscope detects also apatite and dendritic 

 laminae of specular iron, while the hornblendes are entirely decomposed. 



The middle group consists mainly of andesitic rocks, which form 

 sharp, jagged peaks on either side of the wagon-road, but to the south, 



