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In Europe beds of primitive limestone are generally observed in the mica-slates; but we find also saccharoidal limestone in gneiss of the most ancient formation, in Sweden near Upsala, in Saxony near Burkersdorf, and in the Alps in the road over the Simplon. These situations are analogous to that of Caracas.
This same phenomenon has been remarked by Von Buch in Sweden; but in the temperate parts of Europe garnets are in general contained in serpentine and mica-slates, not in gneiss. In the walls which enclose the gardens of Caracas, constructed partly of fragments of gneiss, we find garnets of a very fine red, a little transparent, and very difficult to detach.
It is bounded on the north by the granites of the Upper Palatinate; and on the south by Alpine limestone, transition-thonschiefer, and the mica-slates of the Tyrol. We arrived, on the 23rd of July, at the town of Nueva Barcelona, less fatigued by the heat of the Llanos, to which we had been long accustomed, than annoyed by the winds of sand which occasion painful chaps in the skin.
The trachytes and basalts of Popayan are separated from the system of the volcanoes of Quito by the mica-slates of Almaguer; the volcanoes of Quito from the trachytes of Assuay by the gneiss of Condorasta and Guasunto.
The two most northerly chains are primitive, and contain the mica-slates of Macanao, and the San Juan Valley, of Maniquarez, and of Chuparipari. These we shall distinguish by the names of Cordillera of the island of Margareta, and Cordillera of Araya.
This group, however, is a hundred leagues long and eighty broad; and though wherever M. Bonpland and I traversed this vast group of mountains, its structure seemed to us extremely uniform, it would be wrong to affirm that it may not contain very metalliferous transition rocks and mica-slates superimposed on the granite.
But the irruptions of the Caribbean Sea having apparently overwhelmed, at a very remote period, a part of the mountains of the shore, the ranges or partial chains are interrupted and some basins have become oceanic gulfs. That island, those of Los Testigos, Marguerita and Tortuga constitute, with the mica-slates of the peninsula of Araya, one and the same system of mountains.
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