354 ORIGIN AND DEVELOPMENT OE OEE-DEPOSITS. 



from the rocks in percolating through them. Mr. Hunt appears 

 to have been considering particularly the veins of copper, but 

 not at all to the exclusion of other veins. 



Professor Ramsay suggested a similar origin for certain 

 lead- veins in the following terms. " It had long been shewn that 

 in Derbyshire fissures in anticlinals were unproductive, but 

 those in synclinals productive of lead-ore, and this was explained 

 by the lead (of the rocks) being dissolved by the water falling 

 at the surface, which, travelling along the planes of stratification 

 conveyed it from the convexities and towards the hollow folds of 

 the beds."* Mr. De Eance said the same explanation applied to 

 the lead veins of Alston Moor, which Mr. Wallace had described 

 in 1861, and at the same time had suggested a similar leaching- 

 out process.! 



Each of these writers, it will be observed, assumes the 

 previous existence of the copper and lead in the rocks at or 

 above the level of the deposits referred to, and in such a state as 

 to be leached out by percolating waters. This assumption may be 

 readily admitted in the case of carbonate of lime and other 

 veinstones of group 1, also perhaps in the case of the quartz 

 and other veinstones of group 2. There is also no difficulty in 

 applying it to the vein and joint segregations of oxidized 

 metallic salts, chiefly carbonates, which are seen in the cupriferous 

 sandstones of Alderley Edge, or to the carbonate of lead 

 "pockets" so abundantly found at Leadville in Colorado. 

 Doubtless, the wide-spread existence of such oxidized substances 

 indicates an antecedent probability for the views expressed by 

 Hunt and Wallace. If we could account for the sulphur of the 

 metallic sulphides (group 4), the descension hypothesis would 

 be still more widely applicable, but for this, and perhaps for the 

 metals in combination with it, more deep seated sources or 

 agencies would seem to be necessary. Metallic sulphides as 

 such could hardly be transferred from the parent rock to the lode- 

 fissure by circulating waters under ordinary temperature and 

 pressure, and especially if the waters were neutral or acid, since 

 sulphides under such conditions are either insoluble or are 



* Quart. Jour. Geol. Soc, 135, p. 659. 

 flbid. 



