movements, and to convert them into receptacles of metallic ores, accessible by the labours of man. The greater part of metalliferous veins originated in enormous cracks and crevices, penetrating irregularly and obliquely downwards to an unknown depth, and resembling the rents and chasms which are produced by modern Earthquakes. The general disposition of mineral veins within these narrow fissures, will be best understood by reference to our first Section. (Pl. 1. Figs. k l.—k 24.) The narrow lines which pass obliquely from the lower to the upper portion of this Section, represent the manner in which Rocks of various ages are intersected by fissures, which have become the Receptacles of rich Treasures of Metallic Qre. These fissures are more or less filled with various forms of metalliferous and earthy minerals, deposited in successive, and often corresponding layers, on each side of the vein.
Metallic Veins are of most frequent occurrence in rocks of the Primary. and Transition series, particularly in those lower portions of stratified rocks which are nearest to unstratified crystalline rocks. They are of rare occurrence in Secondary formations, and still more so in Tertiary strata.[1]
- ↑ M. Dufrenoy has recently shown that the mines of Hæmatite and Spathic iron in the Eastern Pyrenees, which occur in Limestones of three ages, referable severally to the Transition Series, to the Lias, and to the Chalk, are all situated in parts, where these Limestones are in near contact with the Granite; and he considers that they have all most probably been filled by the sublimation of mineral matter into cavities of the limestones, at, or soon after the time of the Elevation of the Granite of this part of the Pyrenees. The period of this elevation was posterior to the deposite of the Chalk formation, and anterior to that of the Tertiary Strata. These Limestones have all become crystalline where they are in contact with the Granite; and the Iron is in some places mixed with Copper pyrites, and argentiferous galena. (Mémoire sur la Position des Mines de Per de la Partie orientale des Pyrenees, 1834.)
Awarding to the recent observations of Mr. C. Darwin, the Granite of the Cordilleras of Chili (near the Uspellata Pass) which forms peaks of a height probably of 14,000 feet, has been Enid in the Tertiary period;
