ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 329 



widening of fissures and successive deposition can only go on 

 {a) when the rock is shrinking, or (b) where there is room for 

 the. rock's expansion in some other direction, or (c) when some 

 constituent is progressively dissolved and carried off by the 

 circulating fluid,- or {d) where colloid is being transformed into 

 crystallized matter. As a matter of fact, evidences of all these 

 modes of action are exceedingly common in all ancient rock 

 masses. 



It will be seen, therefore, that the very same portions of 

 fluid may at one time circulate through open fissures of consider- 

 able dimensions (canalicular circulation), at another through very 

 narrow or capillary channels ("capillary circulation), at still another 

 through the potential divisional planes, or between the separate 

 rock constituents (interstitiary circulation) ; the results being 

 different in each case, although there may be no absolute line of 

 demarcation between one form of this circulation and the others. 



The important changes in rocks, known as kaolinization, 

 uralization, serpentinization, schillerization, alunation, &c., and 

 mineralization generally, seem to be due directly and mainly to 

 the interstitiary circulation — all the modifications of force just 

 referred to taking part in the action in turn or together ; some 

 of the combined results of these complex operations must be 

 dealt with in the next section. 



Electricity. The phenomena of the earth's magnetism were 

 referred to the action of electric currents circulating around it 

 by Ampere more than 60 years ago. In 1832 Mr. Robert Were 

 Fox, who had been experimenting for several years in the copper 

 and lead mines of Cornwall, Devon, and Derbyshire, wrote 

 that this hypothesis seemed to him ' ' to derive strong confirma- 

 tion from the stratification of rocks, the arrangement of metallic 

 and other veins, the high temperature which, in a greater or less 

 degree prevails under the surface of the earth, and its rotation 

 on its axis .... I was consequently led to suspect the existence of 

 free electricity in metallic veins, and I was not disajppointed."* 

 The experiments he had undertaken in 1829 at Wheal Jewel and 

 other mines, and reported in a paper read to the Royal Society 



* Proc. Roy. Soc, iir, 1832, pp. 123-125. Phil. Mag., i, 1832, pp. 311-314. 



