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In a thick mass of laminated, feldspathic and altered clay-slate, interposed between two great strata of porphyritic conglomerate in Central Chile, and where there could be but little doubt about the bedding, I observed similar slight differences in composition, and likewise some distinct thin layers of epidote, parallel to the highly inclined cleavage of the mass.
These hillocks consist of purple claystone and of various other porphyries, and of much white feldspathic greenstone passing into andesite; this latter variety included in one case crystals of orthitic and albitic feldspar touching each other, and others of hornblende, chlorite, and epidote.
I nowhere observed mica in this formation, and rarely hornblende; where the latter mineral did occur, I was generally in doubt whether the mass really belonged to this formation, or was of intrusive origin. Calcareous spar occasionally occurs in small cavities; and nests and layers of epidote are common.
Thin layers of feldspar, swelling at intervals into well crystallised kernels, are sometimes included in these black schists; and I observed one mass of the ordinary black variety insensibly lose its fissile structure, and pass into a singular mixture of chlorite, epidote, feldspar, and mica.
This whole great pile of rock has suffered much metamorphic action, as is very obvious in the gradual formation and appearance of the crystals of albitic feldspar and of epidote in the bending together of the fragments in the appearance of a laminated structure in the feldspathic slate and, lastly, in the disappearance of the planes of stratification, which could sometimes be seen on the same mountain quite distinct in the upper part, less and less plain on the flanks, and quite obliterated at the base.
This hill is conspicuous from rising to the height of 6,400 feet: its summit shows a nucleus, uncovered for a height of 800 feet, of fine greenstone, including epidote and octahedral magnetic iron ore; its flanks are formed of great strata of porphyritic claystone conglomerate associated with various true porphyries and amygdaloids, alternating with thick masses of a highly feldspathic, sometimes porphyritic, pale-coloured slaty rock, with its cleavage-laminae dipping inwards at a high angle.
We might go lower still, and show, as Ruskin has shown in his "Ethics of the Dust," the character, habits, and artifices of crystals; their quarrels, and mode of procedure, when a foreign body attempts to oppose their plans, which are more ancient by far than our imagination can conceive; the manner in which they admit or repel an enemy, the possible victory of the weaker over the stronger, as, for instance, when the all-powerful quartz submits to the humble and wily epidote, and allows this last to conquer it; the struggle, terrible sometimes and sometimes magnificent, between the rock-crystal and iron; the regular, immaculate expansion and uncompromising purity of one hyaline block, which rejects whatever is foul, and the sickly growth, the evident immorality, of its brother, which admits corruption, and writhes miserably in the void; as we might quote also the strange phenomena of crystalline cicatrisation and reintegration mentioned by Claude Bernard, etc.
Thus on Wollaston Island slate and grauwacke can be distinctly traced passing into feldspathic rocks and greenstones, including iron pyrites and epidote, but still retaining traces of cleavage with the usual strike and dip.
Near Valparaiso the prevailing rock is gneiss, generally including much hornblende: concretionary balls formed of feldspar, hornblende and mica, from two or three feet in diameter, are in very many places conformably enfolded by the foliated gneiss: veins of quartz and feldspar, including black schorl and well-crystallised epidote, are numerous.
Plagioclase, microcline and quartz are the predominating minerals, while biotite, titanite, epidote, apatite, zircon and garnet are present in smaller quantities. There is also a small amount of hematite, pyroxene and sericite. The rock, which is of a granitic composition, contains numerous crystallites and has been subjected to considerable strain and crushing, which has resulted in foliation.
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