MICA-SLATE, ETC. 883 



the limits here assigned to gneiss, as a predominant rock 

 (long. 68 70|), gneiss passes sometimes to mica-slate, 

 K - hile the appearance of a transition to granite is only found 

 on the summit of the Silla of Caracas.* It would require a 

 more careful examination than I was able to devote to the 

 subject, to ascertain whether the granite of the peak of St. 

 Gothard, and of the Silla of Caracas, really lies over mica- 

 slate and gneiss, or if it has merely pierced those rocks, 

 rising in the form of needles or domes. The gneiss of the 

 littoral Cordillera, in the province of Caracas, contains almost 

 exclusively garnets, rutile titanite, and graphite, disseminated 

 in the whole mass of the rock, shelves of granular limestone, 

 and some metalliferous veins. I shall not decide whether 

 the granitiferous serpentine of the table-land of Buenavista 

 is inclosed in gneiss, or whether, superposed upon that 

 rock, it does not rather belong to a formation of weisstein 

 (heptinite) similar to that of Penig and Mittweyde in 

 Saxony. 



In that part of the Sierra Parime which M. Bonpland and 

 myself visited, gneiss forms a less marked zone, and oscillates 

 more frequently towards granite than mica-slate. I found 

 no garnets in the gneiss of Parime. There is no doubt that 

 the gneiss-granite of the Orinoco ia slightly auriferous on 

 some points. 



(c) MICA-SLATE, with clay-slate (thonschiefer), forms a 

 continuous stratum in the northern chain of the littoral Cor- 

 dillera, from the point of Araya, beyond the meridian of 

 Cariaco, as well as m the island of Marguerita. It contains, 

 in the peninsula of Araya, garnets disseminated in the mass, 

 cyanite, and, when it passes to clayey-slate, small layers of 

 native alum. Mica-slate constituting an independent forma- 

 tion, must be distinguished from mica-slate subordinate to a 

 stratum of gneiss, on the east of Cape Codera. The mica- 

 slate subordinate to gneiss, presents, in the valley of Tuy, 

 shelves of primitive limestone and small strata of graphic 

 ampelite (zeicheschiefer) ; between Cabo Blanco and Catia, 

 layers of chloritic, granitiferous slate, and slaty amphibole ; 



The Silla is a mountain of gneiss like Adam's Peak, in the bland of 

 Ceylon, and of nearly the same height. 



