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PRECIOUS STONES. 9
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main,
for though it was put forward chiefly in connection with certain
Scottish minerals, it covers most, if not all, of the minerals with
which we have to deal, since the majority fall under comparatively few
heads which will be dealt with fully as being more important to our
purpose :— I. Epigene minerals.
A1.—Those
whose first stages consist in their being dissolved at the surface, and
then re-deposited elsewhere outside the lithosphère, (á) Those
deposited on the land. (6) ,, ,, in fresh water.
(c) ,, ,, in closed bodies of water.
(d) „ ,, at the bottom of the sea. A2.—Those whose materials arise through solution
at the surface, and subsequent re-deposition within the lithosphère.
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A3.—Those due to subterranean percolation of waters from the surface.
(a) Those which are altered in situ.
(b) Those whose materials have been
dissolved within the lithosphère, and subsequently re-deposited at lower levels.
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II.
Hypogene minerals. Mostly of hydro-thermal origin, and usually
connected with some manifestation of elevatory movement. B1.—Original minerals of eruptive rocks.
(a) Silicates.
(b) Metals and their compounds.
(c) Other minerals.
B2.—Original contents of mineral veins.
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