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Updated: May 6, 2025
In several parts of Northern Chile this formation extends much further towards the Pacific, over the granitic and metamorphic lower rocks, than it does in Central Chile; but the main Cordillera may be considered as its central line, and its breadth in an east and west direction is never great.
It does not seem probable that the most ancient beds have been quite worn away by denudation, or that their fossils have been wholly obliterated by metamorphic action, for if this had been the case we should have found only small remnants of the formations next succeeding them in age, and these would always have existed in a partially metamorphosed condition.
Third and fourth, two divisions have been organized to prosecute work on the archæan rocks, embracing within their field not only all rocks of archæan age, but all metamorphic crystalline schists, of whatever age they may be found. The first division has for its chief Prof.
The sandstone of the Blue Mountains evidently having been of mechanical origin, and not having suffered any metamorphic action, I was surprised at observing that, in some specimens, nearly all the grains of quartz were so perfectly crystallised with brilliant facets that they evidently had not in their PRESENT form been aggregated in any previously existing rock.
First, that though the strata are generally horizontal, they have been upheaved in Chiloe in a set of parallel anticlinal and uniclinal lines ranging north and south, in the district near P. Rumena by eight or nine far-extended, most symmetrical, uniclinal lines ranging nearly east and west, and in the neighbourhood of Concepcion by less regular single lines, directed both N.E. and S.W., and N.W. and S.E. This fact is of some interest, as showing that within a period which cannot be considered as very ancient in relation to the history of the continent, the strata between the Cordillera and the Pacific have been broken up in the same variously directed manner as have the old plutonic and metamorphic rocks in this same district.
Third, that the protraction of metamorphic decomposition which this beverage produces in the body is chiefly caused by the empyreumatic oil, and that the cafeine only causes it when it is taken in larger quantity than usual.
There, all the different organs of the plant-leaf, blossom, fruit, etc. appear as the metamorphic revelations of the one, identical active principle, a principle which gradually manifests itself to us by way of successive heightening from the cotyledons to the perfected glory of the flower.
Its general course is oblique to the plane of the mountain-face, and the metamorphic slates of which the mountain is built are cut by cleavage planes in such a way that they weather off in angular blocks, giving rise to irregular steps that greatly facilitate climbing on the sheer places.
It consists of gneiss with Labrador-feldspar and feldstones, in all 10,000 feet thick, and both its composition and structure lead us to suppose that, like the Lower Laurentian, it was originally of sedimentary origin and owes its crystalline condition to metamorphic action.
Some of these hornblendic masses may really have been volcanic rocks, which have since assumed a more crystalline or metamorphic texture. SERPENTINE is a greenish rock, a silicate of magnesia, in which there is sometimes from 30 to 40 per cent of magnesia.
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