SALMON — ON THK FORMATION OF OKE-VEINS. 
393 
have originated purely by infiltration, although the first has been 
found in the Freiberg copper-veins and in the Annaberg silver ones ; 
and the spaces, too, of felspar-crystals in the granite of Cornwall can 
evidently have only been filled by infiltration, or sublimation. These 
metals belong, perhaps, principally to certain massive rocks as 
accessoiy constituents, out of the detritus of which are often derived the 
portions of those metals found in washings. Originally they occurred 
in common with the other metals, but it seems to be a peculiar 
characteristic of their nature that they do not occur in pui-ely 
infiltration- veins . 
Notes on the above Memoir. 
As Professor Cotta pre-supposes on the part of his readers a 
general acquaintance with the subject of mineral-veins and the diffi- 
culties which beset the solution of their theoiy, the force of many of 
his observations may not be remarked by those to whom this know- 
ledge is not famiHar. For the benefit of such I have jotted down 
the follomng notes which, while serving to elucidiate this memoir, 
may also be useful as indicating some of the difficulties that beset the 
subject, and some of the more important prehminary problems 
necessary to be solved. 
I. Melation hetween cri/staUine and eruptive roclcs and metalliferous- 
deposits. — Prof. Cotta's reasoning is entirely founded upon the gene- 
rally observed relation between crystalline and eruptive rocks and 
metalliferous deposits. That this relation is a nearly constant fact 
seems to be beyond doubt, although there are occasional exceptions — 
not, however, sufficiently numerous to destroy the force of the ob- 
served relations, which have passed into a proverb in most mining- 
districts. But merely observing the fact of this relation is one thing, 
and accounting for it in a satisfactory manner is another. The first has 
been done universally ; the second has never been seriously attempted, 
and probably, in the present state of our knowledge, is a problem im- 
possible of solution. The most we can do is, as Prof Cotta has done, 
to suggest such a probable hypothesis, as may be useful in giving a 
definite direction to our ideas and to our investigations. 
II. Wlience are the metal-cuntents of ore-deposits derived ? — This 
