32 KEMP'S ORE DEPOSITS. 



the Tombstone district, Arizona, is on a vein which pierces slates, 

 and in one place forty feet of limestone. In the slates it carried 

 high-grade silver ores, with no lead, but in the limestone, lead-sil- 

 ver ores. A rock like limestone might well exercise a precipita- 

 ting action, which, however, we cannot attribute to rocks composed 

 of the more inert silicates. Again, it has been said that the solu- 

 tions coming from below have varied in different portions of the 

 vein or at different periods. An earlier opening would thus be 

 filled with one ore, a later opening with another. This is hy- 

 pothetical, but has been advanced for Klausen by Posepny. (Ar- 

 chiv f. Praktisclie Geologic, p. 482.) A further general objection 

 to the first interpretation of lateral secretion is the weak dissolv- 

 ing power of cold surface waters, and this is a very serious one. 



1.04.08. As opposed to the second interpretation, it may be 

 advanced that precipitation in a cavity at a great depth would be 

 retarded by the heat and the pressure, to just that extent to which 

 solution in the neighboring walls would be aided. The tempera- 

 ture and pressure being practically the same, the tendency to re- 

 main in solution would be great until the minerals had reached the 

 upper regions and filled the cavity by ascension. Under such cir- 

 cumstances ores would only be deposited below, by some such ac- 

 tion as replacement. To the third interpretation no theoretical ob- 

 jections can be made. 



1.04.09. Infiltration by Ascension. On the side of infiltration 

 by ascension, if two veins or sets of veins were found in the same 

 wall rock, but with different kinds of ores and minerals, the con- 

 clusion would be irrefutable that the respective solutions which 

 formed them had come from two different sources below. Thus at 

 Butte, Mont., there is a great development of a dark, basic granite. 

 It contains two series of veins, of which the southern produces copper 

 sulphides in a siliceous gangue, the northern sulphides of silver, 

 lead, zinc, and iron, also in a siliceous gangue, but abundantly associ- 

 ated with manganese minerals, especially rhodonite. No manganese 

 occurs in the copper belt, nor is any copper found in the silver belt. 

 Such results could originate only in different, deep-seated sources. 

 Again, at Steamboat Springs, Nev., and Sulphur Bank, Cal., the hot 

 springs are still in action and are bringing their burdens of gangue 

 and ore to the surface. The former has afforded a long series of 

 metals, the latter chiefly cinnabar. G. F. Becker 1 has shown that 

 the cinnabar probably comes up in solution with alkaline sulphides. 



1 G. F. Becker, " Natural Solutions of Cinnabar, Gold, and Associated 



