THE AMAZON VALLEY. 
421 
to devote to it. The area is so vast, and tlie whole 
country being covered with forests renders natural sec- 
tions so comparatively scarce, that the few distant ob- 
servations one person can make will lead to no definite 
conclusions. 
It is remarkable that I was never able to find any 
fossil remains whatever, — not even a shell, or a frag- 
ment of fossil w^ood, or anything that could lead to a 
conjecture as to the state in which the valley existed at 
any former period. We are thus unable to assign the 
geological age to which any of the various beds of rock 
belong. 
My notes, and a fine series of specimens of the rocks 
of the Rio Negro, were lost, and I have therefore very 
few materials to go upon. 
Granite seems to be, in South America, more exten- 
sively developed than in any other part of the world. 
Darwin and Gardner found it in every part of the inte- 
rior of Brazil, in La Plata, and Chile. Up the Xingu 
Prince Adalbert met with it. Over the whole of Vene- 
zuela and New Granada, it was found by Humboldt. It 
seems to form all the mountains in the interior of Guiana, 
and it was met with by myself over the whole of the 
upper part of the Rio Negro, and far up the Uaupes 
towards the Andes. 
Prom what I could see of the granitic formation of 
the Upper Rio ^egro, it appeared to be spread out in 
immense undulating areas, the hollows of which, being 
filled up with alluvial deposits, form those beds of earth 
and clay which occur, of various dimensions, everywhere 
in the midst of the granite formation. In these places 
