that the line it would
and must choose would be along any continuous and slightly inclined
diagonal, at times crossing the strata of the schists, though generally
preferring to develop itself and egress between the cleavage planes and
dividing seams of the different schistose beds."

He goes on to say, "Another argument to the same end (i.e., the igneous
origin) may be shown from the fact that the auriferous quartz lodes have
exercised a manifest metamorphic action on the adjacent walls or casing;
they have done so partly in a mineralogical sense, but generally there
has been a metamorphic alteration of the rock." Mr. Rosales then tells
his readers, what we all know must be the case, that the gold would be
volatilised by the heat, as would be also the other metals, which he
says, were in the form of arseniurets and sulphurets; but he fails to
explain how the sublimated metals afterwards reassumed their metallic
form. Seeing that, in most cases, they would be hermetically enclosed in
molten and quickly solidifying silica they could not be acted on to
any great extent by aqueous agency. Neither does Mr. Rosales's theory
account at all for auriferous lodes; which below water level are
composed of a solid mass of sulphide of iron with traces of other
sulphides, gold, calcspar, and a comparatively small percentage of
silica. Nor will it satisfactorily explain the auriferous antimonial
silica veins of the New England district, New South Wales, in which
quantities of angular and unaltered fragments of slate from the
enclosing rocks are found imbedded in the quartz.

With respect to the metamorphism of the enclosing rocks to a greater
degree of hardness, which Mr. Rosales considered was due to heat, it
should be remembered that these rocks in their original state were much
softer and more readily fusible than the quartz, consequently all would
have been molten and mingled together instead of showing as a rule
clearly defined walls. It is much more rational to suppose that the
increased hardness imparted to the slates and schists at or near their
contact with the lode is due to an infiltration of silica from the
silicated solution which at one time filled the fissure. Few scientists
can now be found to advance the purely igneous theory of lode formation,
though it must be admitted that volcanic action has probably had much
influence not only in the formation of mineral veins, but also on the
occurrence of the minerals therein.