Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: May 4, 2025
One side of the creek was formed by a spur of mica-slate; the head by a cliff of ice about forty feet high; and the other side by a promontory fifty feet high, built up of huge rounded fragments of granite and mica-slate, out of which old trees were growing. This promontory was evidently a moraine, heaped up at a period when the glacier had greater dimensions.
According to the fabulous stories of the natives, the islets of mica-slate, situate in lake Amucu, augment by their reflection the lustre of the nebulae of the southern sky. How can we infer the absolute sterility of the primitive rocks of Guiana from testimony merely negative, from the circumstance that during a journey of three months we saw no auriferous vein appearing above the soil?
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.
The scenery was remarkable The chief part of the range was composed of grand, solid, abrupt masses of granite, which appeared as if they had been coeval with the beginning of the world. The granite was capped with mica-slate, and this in the lapse of ages had been worn into strange finger- shaped points.
Evidence derived from an inclined stream of lava at the eastern base of the Portillo, might be adduced to show, that it owes part of its great height to elevations of a still later date. Looking to its earliest origin, the red granite seems to have been injected on an ancient pre-existing line of white granite and mica-slate.
It is an inland gulf two miles and a half long from east to west, and one mile broad. The rocks of mica-slate that form the entrance of the port leave a free passage only two hundred and fifty toises broad. The water is everywhere from fifteen to twenty-five fathoms deep.
If we may be allowed to judge of the structure of the whole Sierra Parime, from the part which I examined in 6 degrees of longitude, and 4 degrees of latitude, we may believe it to be entirely composed of gneiss-granite; I saw some beds of greenstone and amphibolic slate, but neither mica-slate, clay-slate, nor banks of green limestone, although many phenomena render the presence of mica-slate probable on the east of the Maypures and in the chain of Pacaraina.
Further east, on the banks of the Arco, and near Cariaco, it seems to gush from secondary limestone formations, but probably that happens only because those formations repose on mica-slate. The hot springs of Venezuela have also their origin in, or rather below, the primitive rocks.
The predominant rock is mica-slate, with thick folia of quartz, very frequently alternating with and passing into a chloritic, or into a black, glossy, often striated, slightly anthracitic schist, which soils paper, and becomes white under a great heat, and then fuses.
These layers have the same direction and the same inclination as the mica-slate of Araya. Where the flank of the limestone mountains of New Andalusia is very steep we observe, as at Achsenberg, near Altdorf in Switzerland, layers that are singularly arched or turned. The tints of the limestone of Cumanacoa vary from darkish grey to bluish white and sometimes pass from compact to granular.
Word Of The Day
Others Looking