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-ievel. 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 arc 
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 ganguc- 
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 
chauges, 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 diflicult to determine the extent to which water is capable 
of acting upon metallic salts or substances, yet the purest metals, when suffi- 
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 be 
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 underwater 200 years.'' " At Wolfclough Mine, 
in the county of Durham, which was closed for more than twenty years, and 
opened again, needles of white lead-ore were observed projecting ft-om 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 tlie 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. 
