248 PROCEEDINGS OF SECTION C. 
sure, as the solutions ascended from lower and hotter levels 
to higher and cooler levels. 
(c) The presence of precipitates for special metals in the 
wall-rock, or in meteoric waters coming from the wall-rock, 
might produce special concentrations of metals where the 
fissure traversed certain rocks. 
(d) Variations m the amount and kind of metamorphism 
which the solutions produce on the wall-rock would resuit 
from the gradual lowering in temperature of the solution, 
and from the fact that certain specially-active mineralising 
agents became exhausted from the solutions. 
(e) Variations in the composition of the vein-minerals 
would be produced in part by the same causes which produce 
variations in the metallic contents, and in part also as a 
direct result of the metamorphism of the wall-rock. Sub- 
stances which are taken into solution from the wall-rock in 
the earlier stages may be deposited from solution during a 
later stage. From this it follows also that substances such 
as fluorine and boron compounds, which are deposited during 
the earlier stages of the journey, may be absent from deposits 
formed at later stages. 
Coming now to the question of the general application of 
the plutonic theory to the origin of the metallic contents of 
fissure-veins, it must be admitted at once that there are a 
great number of types for which little or no evidence in 
favour of the plutonic theory is forthcomig. In this, how- 
ever, the meteoric theory is in even a worse dilemma. 
The only way, as far as I am aware, by which it has been 
sought to prove the meteoric theory in the case of deep- 
seated fissure-veins is by analysing the wall-rock, and proving 
that the same metals which are present in the vein are also 
present in the rock. But this alone, even if it is shown to be 
the case, does not always, or even generally, amount to proof 
that the metal in the vein has been derived from the wall- 
rock. For there are two alternative possibilities. (1) The 
metal content of the wall-rock may have been derived 
as an impregnation from the vein. (2) The metal con- 
tent of the wall-rock may be totally independent of the 
metal content of the vein. The latter possibility has been 
greatly strengthened by the researches of late years, which 
have shown that most rocks contain minute quantities 
of the metals commonly found in veins, and therefore that 
the presence of the same metals in the veins and wall-rock is 
not at all an extraordinary coincidence. For the further 
treatment of this question, I must refer to the very remark- 
able work of J. R. Don*, that indefatigable New Zealand 
* (1) Trans. Am. Inst. Mining Eng., Vol. xxvii., 1898. 
