ORE DEPOSIT THEORIES. 247 
other classes of deposits produced by a subsequent deposition 
from these same waters. 
2. That these latter deposits will be formed largely in the 
great fissures, for these represent the natural channels of 
_ underground circulation. 
3. That the plutonic waters may mingle with the meteoric 
waters, and be carried for long distances before their metallic 
contents are deposited. 
4. That fissure-veins which have derived their metallic 
contents from plutonic waters may contain all the metals 
commonly met with in fissure-veins, and especially copper, 
lead, zinc, silver, and gold. 
5. That fissure-veins of plutonic origin which contain these 
metals are not connected with any one class of eruptive 
rocks to the exclusion of any other class, but may occur in 
connection with all eruptives; and that, further, they are 
not exclusively confined to any one period in the consolida- 
tion of the eruptive rock with which they are connected. 
These conclusions are important, and need a little explana- 
tion. We have seen that the metals, tin, tungsten, bismuth, 
&c., are specially characteristic of granitic emanations, as 
proved by their presence in tin veins, and that titanium, 
nickel, and cobalt are specially characteristic of gabbro ema- 
nations, as proved by their presence in apatite veins; but the 
metals copper, lead, zinc, silver, and gold occur both in 
tin veins and apatite veins. They may vary considerably in 
amount in the two sets of veins, but are not exclusively con- 
fined to either. These metals also occur in veins which 
represent intermediate types between tin veins and apatite 
veins. Further, they all occur, often in considerable 
amounts, in contact metamorphic deposits. 
Thus we see that eruptive emanations containing the 
metals commonly met with in fissure-veins may take place 
either from acid rocks or from basic rocks, and they may 
take place either in the early stages or in the latter stages 
of the consolidation. 
6. Fissure-veins of plutonic origin must vary very greatly 
in their metallic contents, in the character of the vein- 
minerals, and in the nature of the metamorphism of the 
wall-rock. The variations may arise from any of the follow- 
ing causes : — 
(a) The original solutions, emanating from rocks of dif- 
ferent composition, and at different periods during their con- 
solidation, would have different temperatures, different pres- 
sures, different metallic contents, and different chemical pro- 
perties. 
(6) There would be a sequence in the deposition of the 
metals during the gradual lowering of temperature and pres- 
