On Mineral Veins. 231 
it should be remembered that they will not decide the com- 
parative age of the mineral deposits in the veins, but only 
that of the joints on which the veins have been formed, for 
it is possible that these joints may have been in existence 
for unknown ages before they were converted into veins by 
the aggregation of the minerals on the lines of fracture. 
The principal evidence against the theory, that veins are 
formed on the fissures caused by faults, and that these fissures 
have either been opened at once, or by successive stages, 
marking different epochs of disruption, and remained open 
until the material now filling the fissure was deposited, 
will be found in the veins themselves, for few cases can be 
produced where such a mode of formation is possible. 
Mineral veins generally penetrate to a great depth, and 
that not vertically, but with a greater or less underlay 
through strata of varying character. Under these conditions 
it is difficult to see how a fissure a few feet wide, from one 
to two thousand feet in depth, and extending for several 
miles, could remain open for the hundreds, or perhaps 
thousands, of years that would be required to fill it by the 
slow process of deposition from water circulating in the 
fissure, and holding in solution the minerals now consti- 
tuting the vein. 
Even in hard rocks, and with only a small area open at 
one time, the greatest difficulty the miner has to contend 
with, is the keeping of the fissure from closing, by means 
of timber or stone-work, until the contents of the vein can 
be taken out ; and all who have had practical experience in 
working mines will be aware that it is absolutely impossible 
for the above theory to be correct. 
The pressure on the sides of the vein increases rapidly 
with the depth ; and in many of the softer silurian rocks, 
where the smallest fissure would not remain open, we have 
large mineral veins. Take, for instance, the Old Man vein 
at Clunes, which is some five or six feet wide at the surface, 
but in going down swells out to one hundred and twenty 
feet wide, and then contracts again, or rather breaks up, at 
a greater depth. Many cases of a similar kind will be found 
in the quartz mines of Sandhurst, Maldon, and other parts 
of the colony, where the veins occasionally open out and 
form large bunches of quartz. Yet we are asked to believe 
that such huge cavities have remained open during the long 
period of time required to fill them. | 
Still greater is the difficulty of accounting on this theory 
