384 VETEOLEUM SPRINGS. 



and between Caracas and Antimano, the more remarkable 

 phenomenon of veins of gneiss inclosing balls of granitiferous 

 diorite (griinstein). 



In the Sierra Parime, mica-slate predominates only in the 

 most eastern part, where its lustre has led to strange 

 errors. 



The amphibolic slate of Angostura, and masses of diorite 

 in balls, with concentric layers, near Muitaco, appear to be 

 superposed, not on mica-slate, but immediately on gneiss- 

 granite. I could not, however distinctly ascertain whether 

 a part of this pyritous diorite was not enclosed on the banks 

 of the Orinoco, as it is at the bottom of the sea near Cabo 

 Blanco, and at the Montana de Avila, in the rock which it 

 covers. Very large veins, with an irregular direction, often 

 assume the aspect of short layers ; and the balls of diorite 

 heaped together in hillocks, may, like many cones of basalt?, 

 issued from the crevices. 



Mica-slate, chloritic slate, and the rocks of slaty amphi- 

 bole, contain magnetic sand in the tropical regions of 

 Venezuela, as in the most northern regions of Europe. 

 The garnets are there almost equally disseminated in the 

 gneiss (Caracas), the mica-slate (peninsula of Araya), the 

 serpentine (Buenavista), the chloritic slate (Cabo Blanco), 

 and the diorite cr greenstone (Antimano). These garnets 

 re-appear in the trachytic porphyries that crown the cele- 

 brated metalliferous mountain of Potosi, and in the black 

 and pyroxenic masses of the small volcano of Tana-TJrca, at 

 the back of Chimborazo. 



Petroleum, (and this phenomenon is well worthy of atten- 

 tion) issues from a soil of mica-slate in the gulf of 

 Cariaco. Further east, on the banks of the Arco, and near 

 Cariaco, it seems to gush from secondary limestone forma- 

 tions, but probably that happens only because those forma- 

 tions repose on mica-slate. The hot springs of Venezuela 

 have also their origin in, or rather below, the primitive 

 rocks. They issue from granite (Las Trincheras), gneisa 

 (Mariara and Onoto), and the calcareous and arenaceous 

 rocks that cover the primitive rocks (Morros de San Juan, 

 Bergantin, Cariaco). The earthquakes and subterraneous 

 detonations, of which the seat has been erroneously sought 

 Ln the calcareous mountains ,of Cumana, have been felt with 



