426 
GEOLOGY OF 
ance) from each other. The sediment carried down into 
this sea by the rapid streams running down the sides 
of these mountains, would tend to fill up and level the 
deeper and more irregular depressions, forming those 
large tracts of alluvial deposits we now find in the midst 
of the granite districts. At the same time volcanic 
forces were in operation, as shown by the isolated gra- 
nite peaks which in many places rise out of the flat forest 
district, like islands from a sea of verdure, because their 
lower slopes, and the valleys between them, have been 
covered and filled up by the sedimentary deposits. This 
simultaneous action of the aqueous and volcanic forces, 
of submarine earthquakes and marine currents, shaking 
up, as it were, and levelling the mass of sedimentary 
matter brought down from the now increasing surface 
of dry land, is what has produced that marvellous regu- 
larity of surface, that gradual and imperceptible slope, 
which exists over such an immense area. 
At the point where the mountains of Guiana approach 
nearest to the chain of the Andes, the volcanic action 
appears to have been continued in the interval between 
them, throwing up the serras of Curicuriari, Tunuhy, 
and the numerous smaller granite mountains of the 
Uaupes ; and it is here probably that dry land first ap- 
peared, connecting Guiana and New Granada, and forming 
that slightly elevated ridge which is now the watershed 
between the basins of the Amazon and Orinooko. The 
same thing occm’s in the southern part of the continent, 
for it is where the mountains of Brazil, and the eastern 
range of the Bolivian Andes, stretch out to meet each 
other, that the sedimentary deposits in that part appear 
