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Updated: October 6, 2025
Northward of Las Minas, the more regular northerly ranges predominate: from this place to near Polanco, we meet with the coarse-grained mixture of quartz and feldspar, often with the imperfect hornblende, and then becoming foliated in a N. and S. line with imperfect clay-slate, including laminae of red crystallised feldspar with white or black marble, sometimes containing asbestus and crystals of gypsum with quartz-rock with syenite and lastly, with much granite.
John Hopkins sat, after a compressed dinner, in his glove-fitting straight-front flat. He sat upon a hornblende couch and gazed, with satiated eyes, at Art Brought Home to the People in the shape of "The Storm" tacked against the wall. Mrs. Hopkins discoursed droningly of the dinner smells from the flat across the hall.
Here we find greenstone breccia'd with the blackest hornblende; there huge filons of hard, red, heat-altered clays, faced with iron, whilst the fracture is white as trachyte; and there filets of quartz, traversing large curtains and sheets of light-coloured argils.
When we come to study the chemical composition and the microscopical structure of lavas, however, we shall find that there are many respects in which they differ entirely from these artificial products, they consisting chiefly of felspar, or of this substance in association with augite or hornblende.
The hills as well as the valleys were generally covered with good grass, excepting in the scrub. On some of the hills the rocks were shivered into irregular pieces, and displayed crystals of quartz, small laminae of mica, and occasionally hornblende. This evening we camped by the side of a fine casuarina creek, coming from the north-east.
This mountain consists of hornblende rock; in one place, of hornblende slate, with very beautiful large crystals. Copper ores are found in several places in Luzon; and specimens of solid copper were obtained by me at the Bay of Luyang, N. of the Enseñada de Patag, in Caramuan.
These rocks possess an extremely varying character; they consist of black, brown, and grey, compact, basaltic bases, with numerous crystals of augite, hornblende, olivine, mica, and sometimes glassy feldspar. A common variety is almost entirely composed of crystals of augite with olivine. These compact lavas alternate with tuffs, amygdaloids, and wacke, and in some places with coarse conglomerate.
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.
In Syenite quartz is rare or wanting, hornblende taking the place of mica, and the proportion of silica not exceeding 50 to 60 per cent. Granite often preserves a very uniform character throughout a wide range of territory, forming hills of a peculiar rounded form, usually clad with a scanty vegetation.
One of these, which is evidently the second in age, is seen to cut through an older granite; and another, still newer, traverses both the second and the first. In Shetland there are two kinds of granite. One of them, composed of hornblende, mica, feldspar, and quartz, is of a dark colour, and is seen underlying gneiss.
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