THE AMAZON VALLEY. 
423 
burisj which seem rather more extensive, and form some- 
thing more like a connected range of hills. 
But the great peculiarity of them all is, that the 
country does not perceptibly rise to their bases ; they 
spring up abruptly, as if elevated by some local isolated 
force. I ascended one of the smaller of these serras as 
far as practicable, and have recorded my impressions of 
it in my Journal. (See page 218.) 
The isolation and abrupt protrusion of these moun- 
tains is not however altogether without parallel in the 
Andes itself. This mighty range, from all the informa- 
tion I can obtain, rises with almost equal abruptness 
from an apparently level plain. The Andes of Quito, 
and southward to the Amazon, is like a huge rocky 
rampart, bounding the great plain which extends in one 
unbroken imperceptible slope from the Atlantic Ocean to 
its base. It is one of the grandest physical featimes 
of the earth, — this vast unbroken plain, — that mighty 
and precipitous mountain-range. 
The granitic rocks of the Rio Negro in general con- 
tain very little mica ; in some places however that mi- 
neral is abundant, and exists in large plates. Veins of 
pure quartz are common, some of very great size ; and 
numerous veins or dykes of granite, of a different colour 
or texture. The direction of these is generally nearer 
east and west, than north and south. 
Just below the falls of the Rio Negro are some coarse 
sandstone rocks, apparently protruding through the gra- 
nite, dipping at an angle of 60° or 70° south-south- 
west. (Plate I. c.) Near the same place a large slab of 
granite rock exhibits quantities of curiously twisted or 
