HAVALLAH EAKGE. ' 675 



shaped fragments. The prevailing color is a dull earthy gray. It is made up 

 of quartz, feldspar, mica, and some hornblende. The quartz occurs usually 

 in small grains of a dark-gray color, well disseminated through the mass, but 

 rarely as prominent as the feldspar. Both monoclinic and triclinic feldspars 

 are present, although the former are the more abundant ; many of them are 

 well developed, and measure 2 and 3 inches in length, with broad tabular 

 faces and a brilliant lustre. Mica is present as biotite in small dark plates 

 that decompose readily. The hornblende, always in small crystals, is dark 

 green in color, but, in the greater part of the rock, is a very subordinate 

 constituent. In the interstices between the larger crystals and on the 

 broader faces of the feldspars are frequent coatings or thin layers of reddish 

 oxide of iron, which give to the granite an altered appearance, and undoubt- 

 edl};- cause the characteristic weathering. 



Under the microscope, Zirkel has detected in thin sections of the rock 

 large numbers of minute apatites, and inclosed in other crystals particles of 

 magnetite,' and what he regards as probably muscovite. The microscopical 

 examination of the feldspars of this granite is of special interest, and they pre- 

 sent many striking and varied peculiarities in the composition and arrange- 

 ment of the enclosed minerals and microlitic needles. A detailed descrip- 

 tion of these phenomena will be found in Zirkel's report,' accompanied by 

 illustrations. He also shows the close analogy in microscopical structure 

 between these feldspars and those with a somewhat similar habit from a 

 syenite in Southern Norway. The quartz crystals of this. granite are of 

 interest, as three distinct forms of liquid-inclusions have been observed : 

 first, simple aqueous inclusions, with a bubble ; second, simple carbonic-acid 

 inclusions ; third, those containing both water and fluid carbonic acid. 



North of 'Summit Springs, and on the east side of the range, occurs a 

 narrow dike of intrusive granite, which has cut through the older body, and 

 is therefore evidently of later age. As already mentioned, the large body 

 of granite appears to possess many features in common with the Archaean 

 granite of the Rocky Mountains ; but this dike, on the other hand, although 

 we have no structural evidences of its age otherwise than its being subse- 

 quent to the main mass, bears a close resemblance to those eruptive bodies 



^ Microscopical Petrography, vol. vi, 45. 



