THE LODE. 285 



claims for which jiatents have been issued, those on which apphcations for a 

 patent have been made, those determined by U. S. survey, but on which no 

 applications for patents have been made, and finally claims the boundaries 

 of which have merely been determined by private survey. An index to 

 the claims, showing the position of each on the map, will be found at the 

 end of the volume.^ 



Conclusions. — Collccti vcly, tlic various observations made, if they are correct 

 and the inferences from them sound, throw considerable light on the history 

 of the Lode. After the eruption of the diorite the first event of importance, 

 so far as the vein is concerned, was the outburst of diabase, which involved 

 a rupture and dislocation of the earlier diorite, leaving a smooth contact 

 between the two rocks at an angle of about 45°. The contact was after- 

 wards slightly opened to admit the younger diabase or black dike. Erup- 

 tions of earlier hornblende-andesite and of augite-andesite afterwards 

 occurred, which probably caused fractures and dislocation in the eastern 

 portion of the diabase, but produced no traceable action on the Comstock 

 fissure. The country was subsequently so eroded as to reduce the surface 

 of these four i-ocks to a gently sloping plain, with an inclination of a little 

 more than two degrees to the west. After the commencement of the dry 

 period (dry, that is to say, so far as this region was concerned) a great 

 movement began which may possibly have been a sinking of the hanging 

 wall, but was moi'e probably a rise of the foot wall. The center of action 

 appears to have been near Mount Davidson. This dislocation involved an 

 enormous friction, one result of wliicli was a separation of the foot wall and 

 the hanging wall into sheets parallel to the fissure for a long distance from 

 it. A secondary eifect of the same force was the formation of innumerable 

 cracks in these sheets nearly perpendicular to their partings. The edge of 

 the east country necessarily assumed the form of a wedge, and was broken 

 completely through at a point a few hundred feet below that at which the 

 primary fissure reached the surface. Openings were formed along the Com- 

 stock as a result of the movement of the walls, but under a variety of 

 circumstances. In Gold Hill a space was left by the non-confoi'mity of the 

 wall surfaces brought into opposition. In the Virginia group a slight 



' The claim-map was prepared by Messrs. Hotl'manu & Craven. Some additions and corrections, 

 however, were made by Mr. Wrinkle. 



