ORIGIN AND DEVELOPMENT OF ORE DEPOSITS. 129 



an earthen vessel was divided into two water-tight compartments 

 by means of a clay wall of partition. In one cell was placed a 

 mass of copper pyrites, in the other a plate of zinc, and the two 

 were connected by means of a copper wire. The cell in which 

 the copper ore was placed was then filled with a solution of 

 sulphate of zinc, and the other cell with acidulated water, while 

 the clay itself had also been well worked up with acidulated water. 

 After three or four months the clay had become dry, and exhibited 

 a schistose structure parallel to its perpendicular sides, i.e., at 

 right angles to the course of the electric current. One principal 

 line of division was observable near the middle, which seemed 

 to divide the clay into two separate plates, existing in opposite 

 electrical states. When sulphate of iron was used in the cell 

 with the copper-ore, thin bands of oxide of iron were formed ; 

 if sulphate of copper then veins of oxide of copper, besides which 

 specks of oxide of copper were isolated in different parts of the 

 mass. Mr. Fox thought these experiments illustrated the origin 

 of schists, as well as of mineral veins intersecting schists and 

 other rocks." 



The very common schistose structure of clay partings and 

 veins, in lodes and in masses of granite or other rocks near the 

 lodes {sheeting), may very well be due to some form of electrical 

 action as suggested by Mr. Fox. There are many cases in which 

 a mechanical cause would be well nigh impossible. The 

 "schistose-porphyry" and the "porphyritic schist" (altered shaly 

 sandstone) of the Bio Tinto district may not improbably have a 

 similar origin,* and perhaps the schistose structure of rocks in 

 mineral districts generally. It may be observed that true slaty 

 cleavage is very rare in mineral districts, at any rate in those of 

 real value. 



It is obvious from the foregoing that true slaty cleavage, 

 although something quite different from and independent of 

 lamination and foliation, may yet, in some instances, be almost in- 

 distinguishable from them. Thus, in the case of lamination, if the 

 original layers of a fine sedimentary deposit happened to coincide 

 with the direction in which natural forces were producing true 

 slaty cleavage, as must be the case in some portions of a highly 



*J. H. Collins, Geology of the Eio Tinto Mines, p. 251. 



