776 DESCRIPTIVE GEOLOGY. 



tezuma Range; and there can be no doubt of their similar origin and 

 occurrence, the resemblance holding good even when the rocks are sub- 

 jected to the careful scrutiny of microscopical analysis. They are composed 

 of quartz, biotite, and muscovite, and in thin sections under the microscope 

 Zirkel detected still a third mica in thin laminae of an oil-gi'een color. It 

 is somewhat singular that neither in these schists nor in those from the 

 Montezuma Range were traces of feldspar to be found. These beds may, 

 perhaps, be best classed under the head of mica-schists, although they 

 show but little tendency to develop a characteristic schistose structure or 

 parallelism in the arrangement of the constituent minerals. They are, 

 however, distinctly bedded, standing at a high angle, but so fine-grained as 

 to present almost a homogeneous mass to the unaided eye. 



Associated with the mica-schists occurs another rock, which, in its out- 

 ward appearance, bears little resemblance to' the beds of Pah-keah Peak, but 

 which, nevertheless, seems to belong to the same series. It is found on the 

 western ridge near the head of Crusoe Canon. At first sight, it appears like a 

 fine-grained quartzite, but on further examination one is led to doubt this 

 hasty conclusion. Under the hammer, it shows a sharp, angular fracture, 

 but is by no means brittle like most true quartzites. In color, it is a pale- 

 greenish white. Under the microscope, in thin sections, it shows a ground- 

 mass of quartz everywhere penetrated with innumerable minute crystals of 

 hornblende. Feldspars appear to be entirely wanting as in the mica-schist. 

 In this rock, hornblende would seem to replace the dark mica in the rock 

 from Pah-keah Peak. 



The granites, which have been classed as undoubtedly of Archaean 

 age, occupy but a small area on the surface of the Pah-tson Mountains, and 

 were only observed near the head of Crusoe Canon and in the deep cuts 

 of the adjacent lateral ravines. It is very possible that they may be 

 exposed in other localities to a limited extent, especially in the northern 

 end of the mountains; but the great body of the formation is evidently 

 buried beneath the later granite and the great accumulation of volc'anic 

 rocks. In the region of Crusoe Canon occurs a characteristic granite. It 

 has a very much altered, decomposed appearance, a rusty, earthy color 



