REVIEWS. 



453 



" Those portions of a vein," says Mr. Leeds, which from the peculiar con- 

 formation of the country around them are drained of their water, are usually the 

 most unproductive. They appear, like the dead bark upon a tree, to contain no 

 life, and to possess no mineralizing properties. The ores are usually in a state of 

 decomposition, or seeming decay, and the whole metallic appearance is that of a 

 state of decrease. This peculiar condition of the veins above what is technically 

 termed the "water-level," is unfavourable to all except gold-veins. In them the 

 decomp osition of the ferruginous pyrites has had the tendency to liberate the 

 minute particles of gold, and render them more accessible to the manipulating 

 machinery ; but, with this one exception, the veins are not considered valuable 

 above water- level. And it is the very absence of ' vitality,' in the exception just 

 named, that causes this temporary benefit ; for even in gold- veins the ores are 

 more rich at and below water-level, for permanent and enduring work, than they 

 are above it ; but the ores from below the water-level, from their hardness, require 

 more labour to extract the gold. Below the water-level the pyrites remain 

 unchanged, the wall-rock, maintains its primitive induration, and the gangue- 

 stone holds its natural structure. Above the water-level the pyrites will be found 

 altered from its bright, glistening hue and compact structure, through all the 

 changes, from a slight oxidation merely coating its exterior, to an entire decom- 

 position into a soft pulverulent form." 



After quoting from various authors to confirm the truth of this proposition 

 Mr. Leeds divides his investigation of the action of water in veins into these 

 heads : — 1st, Its Properties as a Solvent ; 2nd, Its Mechanical action ; 3rd, Its 

 Electro-magnetic bearing ; and 4th, Its Chemical power. 



Although it may be difficult to determine the extent to which water is capable 

 of acting upon metallic salts or substances, yet the purest metals, when sufii- 

 ciently divided, are soluble in water. It has been shown that silver, mercury, 

 lead, copper, and other metals have been taken up by water and deposited on the 

 surface of rifts, as in the Christiana Mines in Norway, in Peru, and in other 

 mining districts. " When, therefore, water impregnated with sulphur meets the 

 same element charged with metals, permeating the joints and pores of the rocks, 

 precipitation takes place, and a compound is formed in accordance with the laws of 

 affinity. Again, although the process of the formation of metallic matter may bo 

 extremely slow, circumstances are recorded which appear to prove it may be, 

 in some instances, perceptible. Mr. Trebra, director of mines in Hanover, has 

 stated that " he had seen a leather thong suspended from the roof of a mine, 

 coated with silver-ore ; he had also observed native silver and vitreous silver-ore 

 coating the wooden supports left in a mine called Dreyweiber, in the district of 

 Marienburgh, which had been under water 200 years." "At Wolfclough Mine, 

 in the county of Durham, which was closed for more than tAventy years, and 

 opened again, needles of white lead-ore were observed projecting from the walls, 

 more than two inches in length." 



So when veins which have long been kept dry by artificial means, have been 

 allowed to refill with water, and remain so for many years, it has been found, on 

 opening them, that the mineral deposition has again progressed during their 

 interval of repletion. The deposition of copper and silver upon the timbers, or 

 upon leaves floating in old mines, is of frequent occurrence ; and the abundance 

 of mineral springs in all parts of the globe is evidence, also, of the solvent powers 

 of water. In many of them we find solutions of the salts of iron, copper, silver, 

 &c, of sufficient strength for these to be deposited by simple evaporation. 



