STRUCTURE OF RUBY HILL. 49 



either that it is quartz, and was deposited after the formation of the fissure, 

 as under the microscope it exhibits the structure of quartzite. 



Relation of the two fissures to the country rock. — The two fissures, the secondary and 

 main fissures, do not exhibit a width which is in any way proportional to 

 the amount of movement which has taken place along their planes. The 

 main fissure in the Eureka, and other southeastern mines, is very strong, 

 often having a width of 12 feet or more, but in the Richmond and Albion 

 it is scarcely more than a seam, and would naturally not be considered 

 of much importance if the great difference in the country rock on each 

 side of it was not taken into account. The secondary fissure, although it 

 is always accompanied by more or less clay, does not always exhibit abso- 

 lute proof of its nature, and in some places might be mistaken for the 

 ordinary contact of two dissimilar rocks, but when considered as a whole 

 and in conjunction with the narrow strip of quartzite in the Richmond mine 

 the fact that it is a distinct rent in the earth's crust can hardly be disputed. 



Back limestone. — This term is used in reference to the limestone which is 

 found on the foot- wall side of the narrow band of quartzite, which in the 

 Richmond and Albion ground accompanies the secondary fissure. In the 

 cross-cut run into the limestone at the point on the fourth level already 

 mentioned (page 45), the quartzite appears in the roof of the main drift, and 

 is scarcely more than a foot wide. Except that it is mixed more than usual 

 with clay and limestone, it differs in no way from the ordinary quartzite. 

 It has the same pinkish color and friable nature. The back limestone is 

 pulverized almost to a powder at the contact, but becomes more compact as 

 the drift penetrates farther from the fissure. This limestone differs in a 

 great many respects from the limestone which is encountered between the 

 quartzite and shale. It is blackish, breaks with an angular fracture, has a 

 somewhat glassy appearance, and its planes of fracture are lined with quartz 

 or calcite. It is a highly metamorphosed and somewhat silicified limestone, 

 and contains some bituminous matter. As yet no ore of any kind has ever 

 been found in it. Its peculiarities are very characteristic, and it is easily 

 recognizable wherever found. Specimens taken at a depth of 900 feet are 

 not distinguishable from those that have been taken at four. 

 2654 L 4 



