THE COMSTOCK LODE. 39 



propylite, the system of fissures induced by the syenite is maintained. After 

 the cooKng of the propylite overflow, a thin dike of andesite penetrated the 

 contact plane between the syenite and the propylite, and was undoubtedly the 

 first step in the formation of the lode. Contemporaneously with this andesitic 

 fissure, or with those of the main andesitic outflow, the easternfissure was formed. 

 To the western is given the name of contact fissure; to the eastern, since it 

 contains nearly all the silver deposits, is applied the term of ore channel. The 

 submerged base of Davidson not only affected the larger outlines of the lode, 

 but has had a tendency to throw the channel further to the east over each of 

 the fluted projections of its surface. 



The eastern fissure never penetrates the syenite, but dies out to a mere 

 clay seam upon its unbroken front. Throughout the greater part of the lode 

 there is no appearance of a vein below this junction; but at the Hale and 

 Norcross, and in the Gold Hill group, the contact does not occur, the east 

 wall curving into parallelism with the west. The great ore channel, then, is 

 simply a gash from the surface down into the inclined fissure which lies upon 

 the face of the west wall. The vast deposits of silver which have given to 

 these mines their world-wide celebrity, have been almost wholly mined from 

 this gash, or its connected openings. While the vein, as a whole, can only be 

 regarded as a true fissure, since its deep connections are evident from its chem- 

 ical and dynamical conditions, yet that particular fissure which has mainly 

 carried the silver is certainly limited in depth by the west wall. The unim- 

 portant channels of ore which have traversed the propylite horses, lying 

 between the two fissures, are so evidently connected with the main ore 

 channel, and confine themselves so closely to its neighborhood, that they may 

 be considered as its accompaniments and spurs. 



The wedge-like mass of propylite occupying the middle of the lode is 

 considered to be a great horse. It is penetrated with a network of innumer- 

 able seams of quartz and clay, and lines which have evidently been the chan- 

 nels of solfataric action. It is generally in a decomposed and spongy condition, 

 frequently having lost its porphyritic texture. This horse is generally sub- 

 divided by longitudinal fissures, commonly filled with clay, and terminating 

 downward, near the regions of the walls, in mere plates of pasty material. It 

 is also divided by curved, conchoidal fractures, with their convexity to the west. 



