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Bed 11 is at least 800 feet in thickness: it consists of thin layers of whitish, greenish, or more commonly brown, fine-grained, indurated tuffs, which crumble into angular fragments: some of the layers are semi-porcellanic, many of them highly ferruginous, and some are almost composed of carbonate of lime and iron with drusy cavities lined with quartzf-crystals.
Captain Sabino, the former governor of Paracale, a well-informed Filipino, who, at the suggestion of the alcalde, accompanied me, had for some years caused excavations to be carried on, in order to find specimens for a speculator who had in view the establishment of a new mining company in Spain; but the specimens which were found had not been removed, as speculation in mines in the Philippines had, in the interval, fallen into discredit on the Exchange of Madrid; and as yet only a little box full of sand, out of a few small drusy cavities, has been fixed upon and pounded, to be sold as variegated writing-sand, after being carefully sifted.
Being directed to examine the ceiling of the first, it was done with some difficulty and much satisfaction, for there in the center was a most exquisite bit of art work, a circular disk of "drusy" quartz about twelve inches in diameter and having the appearance of a flat rosette of fine black lace, in open pattern with small diamonds thickly strung on every thread; a brilliant, sparkling mass of gems.
It seemed almost as though they had not traced us up the crack after all, in spite of the tell-tale heap of broken fungi that must have lain beneath it. At times the cleft narrowed so much that we could scarce squeeze up it; at others it expanded into great drusy cavities, studded with prickly crystals or thickly beset with dull, shining fungoid pimples.
The granite of Mourne is peculiar in structure, and differs from the ordinary type of that rock in which the silica forms the ground mass. In the case of the granite of the Mourne Mountains, the rock consists of a crystalline granular aggregate of orthoclase, albite, smoke-quartz, and mica; it is also full of drusy cavities, in which the various minerals crystallise out in very perfect form.
The quartz is generally very friable, full of drusy cavities, and broken up into innumerable small pieces that are often coloured black by the peroxide of manganese. The gold is in minute grains, and generally distributed loosely amongst the quartz. Pieces as large as a pin's head are rare, and specimens of quartz showing the gold in it are seldom met with, even in the richest portions of a lode.
This latter rock was in one spot remarkable from being full of drusy cavities, lined with quartz crystals, and arranged in planes, dipping at an angle of 50 degrees to the east, and striking parallel to the foliation of an adjoining hill composed of the common mixture of quartz, feldspar, and imperfect hornblende: this fact perhaps indicates that these volcanic rocks have been metamorphosed, and their constituent parts rearranged, at the same time and according to the same laws, with the granitic and metamorphic formations of this whole region.
The geode taken proved on opening to be especially fine, being filled with pearly white calcite crystals of both the dog-tooth and nail-head forms, and was kindly presented to be added to the collection of cave specimens already purchased in town, to which were also added handsome pieces of "drusy" quartz, cave coral, and tufa and mineral wool.
In another common variety of a finer texture, the aggregating process had gone further, for the whole mass consisted of quite short, parallel, often slightly curved layers or patches, of whitish or reddish finely granulo-crystalline feldspathic matter, generally terminating at both ends in blunt points; these layers or patches further tended to pass into wedge or almond-shaped little masses, and these finally into true crystals of feldspar, with their centres often slightly drusy.
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