384 
PETEOI.FXM SPEIUGS. 
and between Caracas and Antimano, the more remarkable 
phenomenon of veins of gneiss inclosing balls of granitiferoiis 
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, how'ever distinctly ascertain w hether 
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 (Buenarista), the chloritic slate (Cabo Blanco), 
and the diorite or 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 Yana-Urca, 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 orig’ ’ " rimitive 
rocks. They issue 
gneiss 
(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 
in the calcareous mountains of Cumana, have been felt with 
