10 DESCRIPTIVE GEOLOGY. 



of a decidedly reddisli color, and composed of a granular, gray and red 

 quartz, and small tabular crystals of red feldspar. The feldspars are chiefly 

 monoclinic; the triclinic crystals, when observable by the unaided -eye, are 

 quite small. Biotite is rather more frequent than in most of the localities ; 

 it occurs in small black plates, and appears to be segregated in spots, while 

 portions of the hand-specimens are macroscopically entirely free from it. 

 There is also present a second variety of dark mica, which Professor Zirkel 

 has determined by means of the microscope, to be allied to lepidomelane. 

 Under the microscope, Professor Zirkel has shown that the quartz crystals 

 carry liquid-inclusions, while several of them hold saturated salt-solutions, 

 with fine cubic crystals of chloride of sodium. The quartz also contains 

 fine laminae of mica, so minute that fifteen hundred of them were estimated 

 to be present in a space of one square millimetre. The feldspars also 

 inclosed both quartz and mica. 



On the west side of the range, near the head of Dale Creek, and about 

 five miles northwest from Sherman, nearly identical rocks occur. They 

 have, perhaps, a somewhat more intensely red color, due to the ferruginous 

 material in the interstices. The quartz grains have finely- colored varied 

 shades of red, while the mica is not so prominent an ingredient. A chem- 

 ical analysis of the two rocks shows a very marked similarity. The analy- 

 ses were made by Mr. R. W. Woodward. 



No. 1 is from the east side of the range. No. 2 is from the west side. 



Specific gravity in both cases is 2.6. 



No. 1. No. 2. 



SiHca 74.74 76.61 



Alumina 1 12.06 12.45 



Ferric oxide 3.25 1.33 



Lime - '. 0.88 0.84 



Soda 3.33 3.12 



Potassa 5.32 5.42 



Lithia .' trace trace 



Phosphoric acid ^trace trace 



Loss by ignition 0.61 0.53 



100.19 100.30 



