SURFACE GEOLOGY. 7 



cation, and to the occurrence of several faults, an exact statement of its 

 mean dip is impossible. This dip is, however, much less than it would at 

 first appear to be on an examination of its contact with the quartzite, as 

 that has apparently been moved upward along the plane of its contact with 

 the limestone, thereby crowding that rock outward. This is the case on the 

 "northern portion of Prospect Mountain, as well as on Ruby Hill. On the 

 surface this limestone usually has a bluish-gray color. It weathers to a 

 •chalky white, and is corrugated and roughened by the mechanical and 

 ■chemical action of water. In texture it is granular-crystalline, and it is 

 frequently hard and tough. . Underground it exhibits numerous varieties 

 of habitus and color. It appears as calcite, coarse marble, hard white and 

 black limestone, and in the neighborhood of ore bodies is usually stained 

 from a light and dirty yellow to a deep reddish brown by oxides of iron. 

 Considerable masses are often met with which have been crushed to a mere 

 powder, and in the neighborhood of ore bodies it is generally more or less 

 "broken up. Numerous caves and vuggs occur in it, and it everywhere shows 

 the action of water. Breccias of different kinds of limestone, cemented to- 

 gether by calcite, are quite common, and occurrences of that mineral and 

 ■of aragonite are frequently met with in the openings in the rock. This 

 limestone is sometimes found distinctly stratified, and is then usually of a 

 dark bluish-gray color. It everywhere gives evidences of having been sub- 

 jected to immense pressure. 



secret canon sbaie. — The Secret Canon shale overlies the Prospect Mountain 

 limestone, and forms a narrow belt which follows the course of the ridge of 

 Prospect Mountain, and, like the above-mentioned limestone, bends round 

 to the west on reaching Ruby Hill. This shale is of a dull bluish color, 

 except where exposed to the atmosphere it has weathered to a dirty yellow, 

 or where it has been subjected to the action of surface waters through fis- 

 sures underground. It is often disintegrated to a mere clay. It is usually 

 argillaceous, though sometimes it alternates with thin layers of stratified 

 limestone, and the strata are much bent and twisted. 



Hamburg limestone. — The Hamburg limestone does not differ so materially 

 from the Prospect Mountain limestone underground as it does on the sur- 

 face. As far as its physical properties are concerned, the limestone in the 



