248 On Mineral Veins. 
placing a piece of quartz containing iron pyrites in a weak 
solution of chloride of gold, and adding any organic sub- 
stance, when a deposition of gold occurs on the pyrites, but 
none on the quartz. In many places the total amount of this 
ore in the schists is very great, and we can understand what 
a large quantity of gold may be locked up with it. Still in 
localities where the sulphides of iron are not plentiful, or 
where the decomposition of the rock has been so great as to 
allow a considerable proportion of these auriferous sulphides 
to be removed and aggregated with the quartz, rich gold- 
bearing veins will be found below the water line, irrespec- 
tive of the depth. 
When the sulphides in the rocks are completely decom- 
posed, as they are found above the water line and near the 
surface, the gold thus liberated is then in a condition to be 
acted on by other agents, and it is probable that nearly the 
whole of it has been accumulated in the veins, forming the 
rich surface deposits so frequently met with. The rich 
casing or layer of auriferous slate running by the side of the 
quartz, which is occasionally found above the water line, — 
changes below that point into a layer of slate full of aurifer- 
ous pyrites, and an extension of this action to the bounding 
rocks will account for the surface deposits. 
A similar illustration is afforded by the diorite dykes of 
the Wood’s Point district. Near the surface these dykes are 
much decomposed, and in this condition the quartz veins 
traversing them have yielded large quantities of gold ; but 
as the rock becomes hard and compact at a greater depth, 
the gold in the veins decreases, indicating that this decompo- 
sition of the bounding rock and consequent liberation of the — 
contained gold, was necessary to the ageregation of the — 
latter in the quartz veins. The dyke may contain quite as — 
large an amount of gold where the quartz veins are worth- — 
less as 1t does where they are rich, but it will require long © 
ages to pass over before the necessary changes are effected — 
that would render this gold available. "¢ 
The question as to the agency by means of which the 
metals were first disseminated through the rocks is not of — 
such practical importance to the miner as that of the 
formation of the deposits from whence our mineral wealth — 
is directly obtained. Mr. S. T. Hunt, who has carefully — 
investigated this matter, expresses an opinion that the metals — 
have been brought to the surface in solution, and precipi- — 
tated by the agency of organic matter along with the con- 
