398 ORIGIN OF THE MATERIALS IN MINERAL VEINS. 



give off steam and carbonic acid. The silicious deposits have here 

 accumulated in the principal fissure to a thickness of ninety yards in 

 each side of the opening. This silica is sometimes in the condition of 

 chalcedony, but most of it is crystalline. The quartz contains oxides 

 of iron and manganese, and small quantities of iron and copper pyrites. 

 In 1878 this older fissure was opened by a tunnel to a depth of fifty 

 feet below the surface, when the vein stuff yielded cinnabar, from 

 which 3 per cent, of mercury was obtained, while the deposits accumu- 

 lated at the surface, from the overflow of the water, only contain traces 

 of mercury. Similar accumulations of cinnabar occur near the hot 

 springs of Calistoga, at the foot of Mount St. Helena. In the great 

 Comstock lode the vein has the gangue consisting of silica and calcite, 

 and yields silver and gold. At a depth of 2660 feet the water issues 

 from the rock at a temperature of 157 F. These waters contain forty- 

 two grains of solid matter to the gallon, partly sulphates, partly car- 

 bonates, and a little chloride. Hence we may infer that the metallic 

 and non-metallic substances alike have been often deposited in the 

 fissures of ancient faults by the waters of hot springs, and that when 

 the temperature of the water is high, these metals may reach the sur- 

 face, but as a rule the temperature is not sufficient for the surface 

 deposition in quantity of anything but salts of lime and quartz, and 

 in such cases the metals only reach the surface in consequence of sub- 

 sequent denudation of the upper part of the vein stuff. It is well 

 known that nearly all metalliferous veins occur in regions characterised 

 by intrusive igneous rocks, volcanic phenomena, or faults. Such 

 influences, by furnishing the heat required to dissolve the metal, must 

 usually be held accountable for the formation of the veins. 



Mr. J. Baddeley has pointed out that a great circle cutting the 

 equator in 10 E. long, and 170 W. long, and reaching to lat. 45 

 north and south, coincides with the principal gold-producing mines of 

 the world. 



Source of Metals. Nothing can be learned concerning the origin 

 of metals. Hence, there is no greater d priori difficulty in deriving 

 metallic veins from invisible materials in the surface rocks, than 

 there would be in obtaining them from imaginary deep-seated masses 

 of metal. Deep-sea exploration, however, has discovered an unex- 

 pected abundance of manganese in concretionary nodules on certain 

 sea-beds ; and it has long been known that the precious metals exist 

 in the ocean in sufficient quantity to become deposited on the copper- 

 sheathing of ships, and affect its commercial value when removed. 

 Dr. Forschammer, by chemical examination of sea water and certain 

 marine organisms, made a valuable contribution to materials for a 

 theory of mineral veins of segregation. He found the following 

 chemical elements : Oxygen, Hydrogen, Chlorine, Bromine, Iodine, 

 Fluorine, Nitrogen. Sulphur forms salts of baryta, strontia, lime, 

 magnesia ; and Phosphorus remains as phosphate of lime when water 

 is evaporated. Carbon deoxidises the peroxide of iron either to 

 protoxide or sulphide, and thus colours deep-sea sands and clays. 

 Silicon is seen forming the skeleton in the calcined cup sponges of 



