THE LODE. 273 



though movements may have occurred only at long intervals It is pos- 

 sible that the seams of rich ore in the great bonanza represent a deposition 

 posterior to the final cessation of movement. 



Tenor of the ore. — The variatiou in the tenor of ore is probably ascribable to 

 two causes. The general poverty and the auriferous character of the quartz 

 associated with the diorite are probably due to the composition of that rock, 

 which in this locality nowhere secretes argentiferous ores. On the other 

 hand, the fluctuations in the composition of the ore associated with diabase 

 are most likely due to a combination of chemical and dynamical causes. 

 Whatever may have been the actual solubility of the silica and the argen- 

 tiferous compounds of the diabase, under the conditions which prevailed 

 when the solutions were formed, it is in the highest degree unlikely that it 

 was the same. When, by a renewed movement of the hanging wall, fresh 

 material was exposed to solution, either the silica or the silver would dissolve 

 with greater relative rapidity than after prolonged exposure to the solvent 

 action ; and the ore deposited would vary correspondingly. It is also by no 

 means impossible that some of the richer ores have been redeposited, form- 

 ing at the expense of surrounding bodies of lower grade. 



indistinctness of the east wall.— The east Wall is vcry iudistiuct ou this aud on 

 most of the other sections. This is in accordance with the lateral-secretion 

 hypothesis. As has been seen, the fragments of country-rock certainly act 

 as centers of crystallization, and, had the solutions risen from great depths 

 along the fissure, quartz must also have crystallized from both walls equally; 

 but if the solutions percolated from the east into the fissure, this structure 

 would certainly not have resulted unless they passed the wall very gradu- 

 ally and gently. 



c,3y,._The clays of the Comstock appear to be for the most part mere 

 attrition mixtures of decomposed tut not necessarily of kaolinlzed rock, as 

 has been explained in Chapter VI. In this section it is obsei-vable that the 

 horses near the croppings end downwards in clay sheets, and that the clays 

 are most abundant where horse matter lies across the general direction of 

 movement. 



Quart, deposited in openings.— Tho SUbstitUtion hypOthcsis of OrC dcpOsitiOU 



receives, as has been seen, no support either from observation or theory. 

 18 L 



