TRUCKEE RANGE. 805 



in normal granite. The quartz-grains are relatively large and nearly color- 

 less, protruding on the weathered surfaces of the rock above the easily 

 decomposable feldspars. Both orthoclase and plagioclase are present, but 

 the former are much more abundant, possessing a dull opaque surface of a 

 decidedly flesh-red tint, which characterizes the entire rock-mass. All the 

 feldspars have a more or less altered appearance, being frequently covered 

 with an earthy ferruginous material, which seems to form a thin coat or 

 film between the individual crystals, causing rapid disintegration where 

 exposed to atmospheric agencies. The mica occurs as biotite well dissemi- 

 nated throughout the rock. It is worthy of special note that neither horn- 

 blende nor titanite could be detected. Under the microscope, in thin sec- 

 tions, a few small crystals of apatite may be seen ; both the quartz and 

 feldspar are rich in liquid-inclusions. 



On the east side of the range, between 4 and 5 miles to the northeast 

 of the granite locality, occurs a very considerable body of highly crystal- 

 line rocks. Among these, the rock from the summit of Nache's Peak de- 

 serves mention, as it is quite unlike any other in the collection from Nevada. 

 It is an extremely hard tough rock, and possesses a crypto-crystalline 

 groundmass, so fine as to render a determination of the mineral constituents 

 with the ordinary magnifying lens quite impossible, while scattered through 

 it are a few altered feldspar grains and decomposed hornblende crystals. 

 Under the microscope, Zirkel has shown the rock to be made up of plagio- 

 clase and hornblende with a little quartz, and he calls attention to the close 

 resemblance between it and the quarry-rock from Quenast in Belgium, so 

 largely used in the pavement of the streets of Paris. 



South of Nache's Peak are found the crystalline schists already men- 

 tioned as having been referred to the Archsean age. They form a series 

 of dark-colored, thinly bedded mica-schists and light quartzose slates, 

 which are here widely separated from any known beds of similar lithologi- 

 cal habit. The former are composed of minute particles of quartz and 

 both dark and bronze-colored micas, while the latter, presenting a consid- 

 erable variety, show evidences of extreme metamorphism. One character- 

 istic rock is so fine-grained as to suggest to the unaided eye a homogeneous 

 mass, but, under the microscope, is shown to possess a micro-granular base, 



