RUBIDGE — ON METALLIFEROUS SADDLES. 



285 



When the saddles were traced down to any considerable depth 

 the gneiss seemed gradually to lose its laminated character, and 

 assume the form of a highly felspathic granite, which lower down 

 lost all traces of metal. 



It was evident to me, as I stated at the time, that the deposits of 

 ore were due to the surface-actions of water, with what aid from 

 electro -magnetic agency I know not. Some of the rocks acted 

 strongly on the magnetic needle ; but, as most of them contained iron, 

 it might have been owing to that, though all the ores that I tried in 

 one or two mines had no such effect. 



I believe that what I then stated still holds good — that at whatever 

 depth (and it varied considerably) surface- action ceased, the ore 

 disappeared. I mentioned several circumstances to show that even 

 the less soluble ores were acted upon by the water of the district, 

 and that in the case of Van der Stell's mine the surface of the excava- 

 tion has been coated with silicate of copper by permeation through 

 the solid gneiss rock since his time, — 1680, 1 believe. 



Your interesting periodical, though ordered through an agent as 

 soon as I heard of it, only reached me last month. I find that views 

 which I entertained on the nature of granite years ago are fast 

 gaining ground on the continent. I wrote about this to members 

 and officers of the Geological Society at intervals for several years • 

 and, though I did so with the diffidence of one whose position did not 

 entitle him to hold an opinion adverse to those of the leaders in science, 

 1 believe that I said enough to show that, if the igneous theory of gra- 

 nite is abandoned by most geologists ere twenty years elapses, as I 

 believe it will be, I was among the first to give it up, and to show 

 good reasons for doing so. That if the metamorphic theory was 

 true, as applies to gneiss, mica-schist, &c, it was equally true of 

 granite, syenite, and greenstone, I felt quite sure in 1855. That clay- 

 slate passed quietly into mica-schist, chlorite- schist, gneiss, &c, 

 without eruptive rock of any kind, I stated as early. That rocks 

 were changed into quartzite by surface-infiltration, I wrote as my 

 opinion to Sir R. Murchison in the same year. In 1857 I showed 

 good reason to believe that the oversight of this fact had led to great 

 error as to the super-position of our strata. Since then I have 

 proved that strata set down as primitive and separated from the 



