THE AMAZON VALLEY. 
425 
small conical liill behind the town of Santarem, at the 
mouth of the Tapajoz, has all the appearance of being 
a volcanic cone. 
The neighbourhood of Para consists entirely of a 
coarse iron sandstone, which is probably a continuation 
of the rocks observed by Mr. Gardner at Maranham 
and in the Province of Piauhy, and which he considered 
to belong to the chalk formation. Up the Tocantins we 
found fine crystalline stratified rocks, coarse volcanic 
conglomerates, and fine-grained slates. At the falls were 
metamorphic slates and other hard crystalline rocks ; 
many of these split into fiat slabs, well adapted for 
building, or even for paving, instead of the stones now 
imported from Portugal into Para. In the serras of 
Montealegre, on the north bank of the Amazon, are a 
great variety of rocks, — coarse quartz conglomerates, 
fine crystalline sandstones, soft beds of yellow and red 
sandstones, and indurated clay rocks. These beds are 
all nearly horizontal, but are much cleft and shattered 
vertically; they are alternately hard and soft, and by 
their unequal decay have formed the hanging stones and 
curious cave described in my Journal. 
The general impression produced by the examination 
of the country is, that here we see the last stage of a 
process that has been going on, during the whole period 
of the elevation of the Andes and the mountains of 
Brazil and Guiana, from the ocean. At the commence- 
ment of this period, the greater portion of the valleys of 
the Amazon, Orinooko, and La Plata must have formed 
a part of the ocean, separating the groups of islands 
(which those elevated lands formed on their first appear- 
