QUARTZ VEINS. 53 



green color, and with no mica readily visible to the eye. Crystals of 

 ripidolite may often be picked out from it with a knife, and it frequently 

 contains garnets in abundance. In small pieces the rock is flexible, but it 

 has little or no elasticity. 



Associated with the above-mentioned rocks, but of less frequent occur- 

 rence, is true gneiss — silicious mica schist with feldspar. It was seen on 

 French Creek near the stockade, in Custer Park, and at several points in 

 the Harney Peak region. While the occurrence of feldspar in the schist 

 is probably more common in the vicinity of the great granitic region, there 

 is nowhere any evidence of a gradation of the gneissic rock into the granite, 

 but the separation between them wherever observed is sharp and distinct. 

 Gneiss, however, is not an abundant rock, and though its occurrence is 

 mentioned as being more pronounced near the granitic areas, it is not bj^ 

 any means a constant and immediate associate of the granite masses them- 

 selves, but shares the field with the silicious, micaceous, chloritic, and 

 hydrous mica schists. 



Special descriptions of the veins of quartz found in the schistose rocks 

 are given in Mr. Jenney's chapter on Mineral Resources, and little need be 

 said here further than to mention their general conrposition and mode of 

 occurrence. They are very abundant, are always parallel with the stratifi- 

 cation of the schists, and are what may be termed veins of intercalation. On 

 Castle Creek, on the headwaters of Spring Creek, and generally in the 

 western part of the schistose area, they are very numerous, and have 

 nearly always a lenticular shape, swelling out and narrowing down as 

 veins so commonly do. They are not usually traceable for great distances, 

 and are generally narrow, rarely exceeding a few inches in width; a few 

 have a thickness of several feet. The quartz composing them is usually 

 bright, vitreous, and translucent, of a pure white, milky, or brown color, 

 and sometimes very ferruginous. Frequently bunches or lenses of quartz 

 are found in the schists, but these are not of great extent. Some of them 

 are evidently true segregations, while others appear to be silicious deposi- 

 tions coincident in origin with the associated strata. 



Where the veins are highly ferruginous they become converted super- 

 ficially into tolerably pure oxide of iron by the weathering and removal of 



