422 
GEOLOGY OF 
grow tlie lofty virgin forests, while on the scantily co- 
vered granite rocks, and where beds of sand occur, are 
the more open catinga forests, so different in their aspect 
and peculiar in their vegetation. What strikes one most ; 
in this great formation, is its almost perfect flatness. I 
There are no ranges of mountains, or even slightly ele- 
vated plateaus; all is level, except the abrupt peaks that ^ 
rise suddenly from the plain, to a height of from one hun- 
dred to three thousand feet. In the Upper Rio Negro 
these peaks are very numerous. The first is the Serra ? 
de Jacami, a little above St. Isabel ; it rises immedi- [ 
ately from the bank of the river, on the south side, to a y 
height of about six hundred feet. Several others are 
scattered about, but the Serras de Curicuriari are far the t 
most lofty. They are a group of three or four moun- \ 
tains, rising abruptly to the height of near three thou- i 
sand feet ; towards their summits are immense preci- j 
pices and jagged peaks. Higher up, on the same river, I 
is another group of rather less height. On the Uaupes * 
are numerous hills, some conical, others dome-shaped, \ 
but all keeping the same character of abrupt elevations, } 
quite independent of the general profile of the country. 
About the falls of the river Uaupes there are small hills 
of granite, broken about in the greatest confusion. Great 
chasms or bowls occur, and slender piUars of rock rise 
up like dead trunks out of the surrounding forest. Up 
the river Isanna, the Tunuhy mountains are a similar 
isolated group. The Cocoi is a quadrangular or cubical - 
mass, about a thousand feet in elevation, which forms J 
the boundary between Brazil and Venezuela; and be- | 
hind it are the Pirapoco, and the serras of the Caba- | 
r 
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II 
