It is true that mineral veins contain many minerals that could not exist together undecomposed with even a moderate degree of heat; but it is only here contended that the original filling of the lodes was an igneous injection, not that the present arrangement and composition of all the minerals is due to the same action. Since the lodes were first filled they have been subjected to every variety of hydro-thermal and aqueous influence; for the cooling of the heated rocks must have been a slow process, and undoubtedly the veins have often been the channels both for the passage of hot water and steam from the interior, and of cold water charged with carbonic acid and carbonate of lime from the surface, and many changes must have taken place. Auriferous quartz veins have resisted these influences better than others, because neither the veinstone nor the metal is easily altered, and such veins therefore form better guides for the study of the origin of mineral lodes than fissures filled with calc spar and ores of the baser metals, all readily dissolved and re-formed by hydro-thermal agencies. Our mineralogical museums are filled with beautiful specimens of crystals of quartz, fluor spar, and various ores deposited one on the other; and the student who confines his attention to these is naturally led to believe that he sees before him the process by which mineral veins have been filled. But the miner, working far underground, knows that such crystals are only found in cavities and fissures, and that the normal arrangement of the minerals is very different. The deposition of various spars one on the other in cavities is a secondary operation even now going on, and has nothing necessarily to do with the original filling of the lodes; indeed, their arrangement is so different that it helps to prove they have been differently formed. It would take a volume to discuss this question in all its bearings, and as I have already entered more fully into it in another place,* (* "Mineral Veins" by Thomas Belt. John Weale 1861. ) I shall only now give a brief resume of the conclusions I have arrived at respecting the origin of mineral veins. 1. Sedimentary strata have been carried down, by movements of the earth's crust, far below the surface, covered by other deposits, and subjected to great heat, which, aided by the water contained in the rocks and various chemical reactions, has effected a re-arrangement of the mineral contents of the strata, so that by molecular movements, the metamorphic crystalline rocks, including interstratified granites and greenstones, have been formed. 2. Carried to greater depths and subjected to more intense heat, the strata have been completely fused, and the liquid or pasty mass, invading the contorted strata above it, has formed perfectly crystalline intrusive granites and greenstones.