Crawrorp.—On the Origin of Mineral Veins. 561 
contained in sea water may be precipitated and retained within the fissures 
or veins. 
If the theory is correct, then the fact is established that silurian rocks 
have been formed in very deep seas at a greater depth than 2,000 fathoms. 
The point which seems to me to be most in favour of the theory is this : 
We find that the chalk formation goes on at a depth of 2,000 fathoms. We 
find no mineral veins in that part of this formation which has been raised 
into dry land. To raise an extended stratum from a depth of 2,000 fathoms 
to a height of some hundreds or thousands of feet above the sea, seems neces- 
sarily to involve many fractures, therefore, prima facie, we might expect to 
find mineral veins. As we do not find any, I think we are entitled to draw 
this conclusion, viz., that the depth of 2,000 fathoms is insufficient for the 
produetion of mineral veins, inasmuch as it does not produce the required 
hollow for the collection of carbonic acid. Similar remarks to those made 
with regard to the chalk may be made of the nummulitic limestone, which 
occupies so large an area in Africa and Asia, and also with regard to other 
roeks, both secondary and tertiary. ; 
The theory therefore stands thus: That the filling of veins or fractures 
by metallic minerals has chiefly taken place at a depth of about 2,500 
fathoms or over; that the precipitating agent has been the carbonic acid 
always present atthose depths; and that precipitation may have proceeded 
either from metals present in the waters of the ocean, or in gases or heated 
water rising from below. 
We may therefore suppose that the formation of mineral veins may be 
always proceeding at the depth already pointed out; possibly collecting fresh 
stores for a time, when the present mines are worked out and the present 
continents have passed away. I have not sufficient chemical knowledge to 
be able to work out this theory in detail, therefore only give it as a general 
idea of the probabilities. It may be objected that metamorphism is a neces- 
sary preliminary or adjunct to the presence of metallic veins, but as a 
matter of fact the most highly metamorphosed rocks are not the most 
abundant in metallic minerals. 
Art. LXXXVII.—On probable reasons why few Fossils are found in the Upper 
Paleozoic, and possible Triassic Rocks of New Zealand. By J.C. Crawrorp, F.G.S. 
[Read before the Wellington Philosophical Society, 16th September, 1876.] 
Tue Upper Paleozoic Rocks occupy a great area in New Zealand. In 
Wellington and Hawke Bay they form the whole of the true mountain 
ranges, Tararua, Rimutaka, Ruahine, ete.; and in Auckland these ranges 
u2 
