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This road is cut out of a talcose gneiss* in a state of decomposition. Travellers suffer from the dust in winter, while in the rainy season the place is changed into a slough. On descending the table-land of Buenavista, about fifty toises to the south-east, an abundant spring, gushing from the gneiss, forms several cascades surrounded with thick vegetation.

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.

The country abounded with pieces of gneiss with a very straight cleavage, that suited them admirably for building purposes. All the granaries of this country were supported upon pillars formed of single stones, about three feet long. The houses were also protected by large flat stones arranged like tiles around the base, and thus securing the sides from the driven storms of rain.

The path was narrow and difficult in the wood, and especially along the bed of the stream, where grew ugly trees of larch, eighty feet high, and abundance of a new species of alpine strawberry with oblong fruit. At 11,560 feet elevation, I arrived at an immense rock of gneiss, buried in the forest.

At length I felt the fresh breeze and drank the invigorating air of the limestone plateau. Descending the hill beyond, on the road to Rodez, I passed a very strange-looking spot where huge flat blocks of bare gneiss, laid together as though giants of the Titanic age had here been trying to pave the world, sloped with extraordinary regularity towards the highway.

In hollowing the new road out of the rock, two large veins of gneiss were discovered in the mica-slate. They are nearly perpendicular, intersecting all the mica-slate strata, and are from six to eight toises thick. These veins contain not fragments, but balls or spheres of granular diabasis,* formed of concentric layers.

In the central region the gneiss is covered by transition or sub-metamorphic rocks, consisting of a strong band of quartzites overlying a mass of earthy schists.

The highly crystalline nature of the rocks, at these great elevations, is due to the action of veins of fine-grained granite, which sometimes alter the gneiss to such an extent that it appears as if fused into a fine granite, with distinct crystals of quartz and felspar; the most quartzy layers are then roughly crystallized into prisms, or their particles are aggregated into spheres composed of concentric layers of radiating crystals, as is often seen in agates.

All the rocks were gneiss and granite, with radiating crystals of tourmaline as thick as the thumb.

The cliff was not 100 yards long, and was about 70 thick; its surface was shivered by frost into cubical masses, and glacial boulders of gneiss lay on the top. The limestone rock was chiefly a blue pisolite conglomerate, with veins and crystals of white carbonate of lime, seams of shale, and iron pyrites.