364 REPORT— 1869. 



Carboniferous Limestones, the veins of which yield a considerable proportion 

 of our lead, calamine, and iron-ore ; and chemical analysis will show that the 

 constituents necessary to the production of these minerals are almost entirely 

 absent from them over the widest areas. The limestones that come nearest 

 in contact with the walls of strong mineral lodes ought, with this view, 

 to yield the best evidence that the minerals have been thus segregated to- 

 gether ; but it wiU be found that they are as free from the minerals that are 

 in the veins as would be samples taken at any distance from the fissures. 



Under this head it is desirable I should notice a view lately suggested by 

 Mr. "Wallace. This gentleman has lately published an elaborate work on 

 ' The Laws which regulate the Deposition of Ores in Veins,' which, though 

 having special reference to the Alston-Moor district, is proposed by him as a 

 law explaining the ore-deposits in all mineral veins. His work shows an 

 intimate knowledge of the complicated physical details of that extensive 

 mining-region, in which, in opposition to sublimation, he remarks, that all 

 the lead-veins are found most productive where furthest removed from the 

 seat of Plutonic action, the richest deposits being in the upper part of the 

 Carboniferous Limestone where no igneous rocks are found, and that in that 

 district there is nothing to support the theory that lead is due to exhalations 

 from below, or to matter injected in a fluid state among the consolidated 

 sedimentary rocks. Instead of this he states that the more probable cause 

 of the lead-ore at Alston is owing to segregation from, or decomposition 

 of, the rocks which form the walls of the veins where they are found. In 

 adopting the doctrine of segregation, he proposes, for the first time, to com- 

 bine with it another cause, without which there would be no important de- 

 posits of minerals, viz. that of recent hydrous and atmospheric agency. 

 Without the passage of large bodies of water downwards from the surface, 

 derived from the rainfall of the district, and their free circulation in the 

 veins, there would be no conditions favourable to the deposit of minerals ; 

 in aU cases he states such deposits are found only where fluids most freely 

 percolate the surface and circulate in the veins, and that these conditions 

 only occur where the strata are situated at moderate depths from the sur- 

 face, and at some considerable distance from the watershed of the moun- 

 tain ; that, combined with electrical action, these agents have been the means 

 of extracting the minerals from the adjoining rocks ; that the operation is 

 still in progress, and that aU has been accomplished since the Glacial period. 



The examination I have given to mineral veins and their contents does not 

 support this view. The chief material of all mineral veins I find to be of 

 mariae origin ; all the organic contents are fossil, and their precise geologi- 

 cal age can be arrived at Avithout much difiiculty. Wherever they contain 

 land shells, as on the Mendips, or freshwater shells, which occur in the 

 veins of Alston, and are wide-spread elsewhere, they are also fossU and of 

 contemporaneous age with the other remains*. It is certain from this that 

 the veins received their infilling when within the influence of the ocean, and 

 before their present elevation, since which time, as I have before stated, I 

 doubt if there could be any material alteration in their contents. 



But supposing their vein-stuff to be postglacial, and that their deposit had 

 been efi'ected by large bodies of water passing down through them from the 

 surface, ample evidence would have been present of the fact ; for in the place 

 of fossU organic remains, which in some instances indicate the exact age of 

 the minerals, there would have been found recent land and freshwater 



* See remarks on the presence of Land and Freshwater Shells, p. 369. 



