76 
3 TEAT A OF GNEISS. 
The zone of gneiss just mentioned is, in the coast-chain 
from the sea to the Villa de Cura, ten leagues broad. In 
this great extent of land, gneiss aud mica-slate are found 
exclusively, and they constitute one formation.* Beyond 
the town of Villa de Cura and the Cerro de Chacao the 
aspect of the country presents greater geognostic variety. 
There are still eight leagues of declivity from the table-land 
of Cura to the entry of the Llanos ; and on the southern 
slope of the mountains of the coast, four different forma- 
tions of rock cover the gneiss. We shall first give the 
description of the different strata, without grouping them 
systematically. 
On the south of the Cerro de Chacao, between the ravine 
of Tucutunemo and Piedras Vegras, the gneiss is concealed 
beneath a formation of serpentine, of which the composition 
varies in the different superimposed strata. Sometimes it 
is very pure, very homogeneous, of a dusky olive-green, and 
of a conchoidal fracture : sometimes it is veined, mixed with 
bluish steatite, of an unequal fracture, and containing 
spangles of mica. In both these states I could not discover 
in it either garnets, hornblende, or diallage. Advancing 
farther to the south (and we always passed over this ground 
in that direction) the green of the serpentine grows deeper, 
and feldspar, and hornblende are recognised in it : it is 
difficult to determine whether it passes into diabasis or 
alternates with it. There is, however, no doubt of its con- 
* This formation, which we shall call gneiss-mica-slate, is pecu- 
liar to the chain of the coast of Caracas. Five formations must be dis- 
tinguished, as MM. von Buch and Raumer have so ably demonstrated 
in their excellent papers on Lundeck and the Riesengebirge, namely, 
granite, granite-gneiss, gneiss, gneiss- mica-slate, and mica-slate. Geo- 
logists whose researches have been confined to a small tract of land, , 
having confounded these formations which nature has separated in several 
countries in the most distiact manner, have admitted that the gneiss and 
mica-slate alternate everywhere in superimposed beds, or furnish in- 
sensible transitions from one rock to the other. These transitions and 
alternating superpositions take place no doubt in formations of granite- 
gneiss and gneiss-mica-slate ; but because these phenomena are observed 
in one region, it does not follow that in other regions we may not find 
very distinct circumscribed formations of granite, gneiss, and mica-slate. 
The same considerations may be applied to the formations of serpentine, 
which are sometimes isolated, and sometimes belong to the eurite, mica- 
shite, and griinstcln. 
