FISSURE SYSTEM. 317 



gether with ore. Where the disturbance has been less extensive and irreg- 

 ular, clean-cut fissures may sometimes be seen fiUed with ore, and these 

 can only bo classed as veins, though they are not persistent. As already 

 mentioned, impregnations also exist where the ore-bearing solutions have 

 encountered permeable sandstones. 



The classification of the various portions of such a deposit under various 

 names seems to me of very little interest, ex(;epting as it serves to a certain 

 extent as a basis of comparison between ore deposits of diff'erent regions. 

 It is not long since it was customary to maintain that the deposits of cinna- 

 bar w^ere very different in character from those of other ores and that the 

 genesis of quicksilver deposits was essentially unlike that of other metals. 

 I have taken some pains therefore to show that no distinction can be main- 

 tained as to form between the ore bodies of the quicksilver mines and well 

 recognized types of gold, silver, and copper deposits. The only important 

 mode of occurrence of ores which I have not encountered in the quicksilver 

 mines is that of replacement. Lead ores have certainly in some cases re- 

 placed limestone molecule for molecule. According to Prof von Groddeck, 

 cinnabar ore at Mt. Avala, in Servia, has replaced serpentine in a similar man- 

 ner. Others also have been led to suppose analogous substitutions at Al- 

 maden and at Idria, but T have not met with tliem at those mines or an\'- 

 where in California. 



Existence of a fissure system. — While thc reference of deposits to different heads 

 of more or less artificial classifications is only of indirect interest, a compre- 

 hension of the fundamental structural relations of the ore bodies of a mine 

 is of the utmost importance to its conduct. From any one accessible stope 

 of the New Almaden mine it is evident that the country has been intersected 

 by fissures, that energetic motion has taken place along these fissures, that 

 the adjoining rock masses have been shattered more or less irregularly, and 

 that solutions entering the ground have deposited ore in such spaces as were 

 vacant. It is also apparent from the relations of the ore to the clay that the 

 solutions have entered from l)elow, and it is almost a necessary inference 

 that the fissures served as channels of ingress for the solutions. These con- 

 clusions may be di-avvn in each of as many chambers as the observer can 



