24 GEOLOGY OP THE COMSTOCK LODE. 



throughout the extent of the vein it is most likely that the portion which 

 lies next to the foot wall will continue unproductive, as it did from the sur- 

 face down to the lowest works, while the entire portion between it and the 

 hanging- wall must be considered as the probable future source of ore. As 

 remarked in the foregoing pages, it is also probable that repeatedly, in fol- 

 lowing the Lode downwai'd, branches will be found rising from its main 

 body vertically into the hanging wall, and consisting of clay and quartz. 

 Many of them will probably be ore-bearing. Such bodies of ore should be 

 sought for at all mines, in what is generally supposed to be the eastern 

 country. Expei-ience in the upper levels would lead to the supposition that 

 such eastern bodies might carry richer ores than the average of the main 

 portion of the vein. 



7th. That the intervention of a barren zone, as is reported by good 

 authorities to occur at the Veta Madre of Guanajuato, at the depth of 1,200 

 feet, is not at all likely to be met with in the case of the Comstock Lode. 

 The argument which we have to adduce for this conclusion has some weight 

 from a geological point of view. It is a well-known fact that the inclosing 

 rocks have usually great influence on the quantity and quality of the ores 

 of certain metals in mineral veins, and that a rich lode passing into a differ- 

 ent formation frequently becomes barren or poor. At the Veta Madre of 

 Guanajuato a sudden decrease in the yield of the ore, at the depth of 1,200 

 feet, attends the passage of the lode into a different formation, which from 

 thence continues to the lowest depth attained. No such change can ever 

 be anticipated for the Comstock Lode, since the structure of the country 

 seems to indicate the continuity of the inclosing rocks to an indefinite 

 depth. 



King's memoir. — lu 1867-'H8 Mr. Clarencc King, Geologist-in-charge of 

 the Exploration of the Fortieth Parallel, made an examination of the Com- 

 stock LoDF.^ In regard to lithology Mr. King mainly followed Baron v. 

 Richthofen, but he recognized a much greater area of andesite than his 

 predecessor, and the affinity between certain propylites and andesites. Of 

 the latter he says: "The balance of probability points to a close alliance 



' Exploration of the Fortieth PaniUel, Vol. III. 



