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Updated: July 19, 2025
Hence, from the southern part of Tres Montes to the northern end of Chiloe, a distance of 300 miles, we have closely allied rocks with their folia striking on an average in the same direction, namely between N. 11 degrees and 22 degrees W. Again, at Valdivia, we meet with the same mica-schist, exhibiting nearly the same mineralogical passages as in the Chonos Archipelago, often, however, becoming more ferruginous, and containing so much feldspar as to pass into gneiss.
Then came tall heather and bracken, dwarf oak and chestnut, box and juniper, all luxuriating about the blocks of mica-schist, a rock that holds water and is therefore conducive to a varied and splendid vegetation, wherever a soil can rest upon it. Towards the summit the trees and shrubs dwindled away, and then came the dry thyme-covered turf scenting the air.
The following may be enumerated as the principal members of the metamorphic class: gneiss, mica-schist, hornblende-schist, clay-slate, chlorite-schist, hypogene or metamorphic limestone, and certain kinds of quartz-rock or quartzite.
Its great antiquity was inferred from its mineral texture, from the absence of fossils, and its passage downward into talc-schist and garnetiferous mica-schist; these rocks again graduating downward into gneiss, which is penetrated, at Forno, by granite veins.
But the same mode of transport can scarcely be imagined for those fragments of mica-schist, one of them weighing from 8 to 10 tons, which were observed much farther south by Mr.
Thus was gradually produced the formation of mica-schist, the mica imperfectly recrystallizing or being merely aggregated together in horizontal plates, between which the quartz either spread itself generally in minute grains or unified into crystalline nuclei.
Not every formation affords the necessary ledges upon which the egg can be deposited with safety the face of the cliff may be too smooth, or too jagged, or the shelves may run at too acute an angle. Many of the large assemblages of Guillemots in the British Islands are found where the rock is quartzite, mica-schist, limestone, or chalk.
The mica-schist here consists of thick layers of quartz, with intervening folia of finely-scaly mica, often passing into a substance like black glossy clay-slate: in one spot, the layers of the quartz having disappeared, the whole mass became converted into glossy clay-slate. Where the folia were best defined, they were inclined at a high angle westward, that is, towards the range.
We saw in the mountains of Upper Orinoco, or of Parime, only granular granites containing a little hornblende, granites passing into gneiss, and schistoid hornblendes. Has nature repeated on the east of Esmeralda, between the sources of the Carony, the Essequibo, the Orinoco, and the Rio Branco, the transition-formation of Tucutunemo reposing on mica-schist?
The rocks were now of gneiss and mica-schist, and the mica was so abundant as to cause many a crag and heap of shale to glitter in the sun, as though there had been a mighty shattering of mirrors here into little particles which had fallen upon everything. There was, however, no lack of contrast.
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