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Updated: June 1, 2025
Leaning out over the polished wooden bar which topped the ironwork of the window-guard Damaris sought and gained sight of the sea. This, darker even than the tufted foliation of the pines since still untouched by sunlight spread dense and compact as molten metal, with here and there a sheen, like that of the raven's wing, upon its corrugated surface. To Damaris it appeared curiously forbidding.
The metamorphic and plutonic formations of the several districts visited by the "Beagle" will be here chiefly treated of, but only such cases as appear to me new, or of some special interest, will be described in detail; at the end of the chapter I will sum up all the facts on cleavage and foliation, to which I particularly attended. BAHIA, BRAZIL: latitude 13 degrees south.
A dense fog obscured all minds, and the dazzling truth could not pierce it; thus all progress in embryology was precluded. Fifty years had passed, and Wolff, poor and persecuted, had died at Petrograd, an exile from his native land, when Pander and Ernest von Baer grappled anew with the theory of "blastodermic foliation."
As in some cases it appears that where a fissile rock has been exposed to partial metamorphic action, for instance from the irruption of granite, the foliation has supervened on the already existing cleavage-planes; so perhaps in some instances, the foliation of a rock may have been determined by the original planes of deposition or of oblique current-laminae: I have, however, myself, never seen such a case, and I must maintain that in most extensive metamorphic areas, the foliation is the extreme result of that process, of which cleavage is the first effect.
There are, however, several other varieties of gneiss regularly foliated, and alternating with each other in so-called strata. The lines of mountains, but not always each separate hill, range nearly in the same direction with the foliation and so-called stratification, but rather more easterly.
In these volumes I have often used the more familiar term of stratification, for foliation. Our ponies unconcernedly scraped away the snow with their hoofs, and nibbled the scanty herbage.
The minerals of which it is composed, and the new minerals which develop by heat and pressure, arrange themselves along planes of cleavage or of shear in rudely parallel leaves, or FOLIA. Of this structure, called FOLIATION, we may distinguish two types, a coarser feldspathic type, and a fine type in which other minerals than feldspar predominate.
In certain spots large quartz veins were numerous, and near them, the cleavage, as was the case with the foliation of the schists in the Chonos Archipelago, became extremely tortuous.
All these spaces are of some depth; each has in the centre a pendant, and in each the opening is fringed with tracery or foliation. In some are elaborate Gothic cuspings, in others long carved leaves curved at the ends; and in one which happens to come exactly over an iron tie-rod for the rods are placed quite irregularly the pendant is much longer and is joined to the tie by a small iron bar.
One form, indeed, that of the cockle, has been in all ages used as the decoration of half domes, which were named conchas from their shell form: and I believe the wrinkled lip of the cockle, so used, to have been the origin, in some parts of Europe at least, of the exuberant foliation of the round arch.
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