RIVER-DEPOSIT OF THE AMAZON. V1 
This rests upon 20 feet of Tertiary clays of the Eocene for- 
mation. 
From a careful study of these recorded sections, I think it is only 
possible to arrive at the conclusion that they have been deposited by 
river-action. The absence of imbedded fossil shells, the great and 
persistent instances of false-bedding, and the non-continuity of the 
beds favour greatly the supposition that the materials of this deposit 
were produced by the wearing action of the Amazon and its tribu- 
taries, and by them deposited in their valley, as they eroded its sur- 
face, on the way to the ocean. 
Examining with attention the action of this great river on the 
line of country through which it flows, we find that as it moves on- 
ward in any one portion of its course it cuts away the materials 
composing its banks on the convex side of its bends; while at the 
same time it deposits near its opposite shore, in the concave curves, 
false-bedded irregular layers of clay and sand derived from materials 
so cut away from places higher up its course; that, owing to its 
curving course, the deepest portion, with its greatest volume, exer- 
cising the most powerful eroding action exerted by any part of its 
width is on one side, while at a distance of a few miles higher up 
or lower down it is on the opposite side. Thus slowly, but surely, 
is it widening out its present valley by encroaching on its banks in 
opposite directions. Upon the side opposite to where the current is 
the cutting-action is absent, and the water has but slight move- 
ment, allowing materials in suspension to be deposited steadily there 
upon its bottom, and gradually filling up its bed, forming a sloping 
foreshore, which is seen when the waters are low. Thus layers of 
mud and sand spread themselves out over the river’s bottom, being 
thick near that side, and thinning off towards mid-river as they come 
within the influence of the rapidly flowing current, and add to the 
growth of the level alluvial tract now being laid down by the river. 
Of course there are excepticns to this rule where the river flows in 
a perfectly straight course in the general direction, and has one or 
more deep-bed channels; but this does not affect the above-described 
general conduct of river-action ; for as the curved portions of the 
river advance they efface and destroy the straight portions, and force 
the whole to assist in the general work of destruction and re- 
modelling. The alluvial tract is below the level of the river’s 
surface in times of flood, so that it is then covered with a sheet of 
currentless water laden with sediment, which, settling down as layers 
of loamy matter, year after year, forms at last a thick covering of 
homogeneous structure. 
Thus two great works are now being performed by the Amazon 
at the same time, viz. the cutting away of portions of the deposit 
which it formerly laid down, and which is the subject of this paper, 
and redepositing the materials so obtained in a thick layer of recent 
alluvium at a much lower level. From a study of the present depo- 
sition of the recent alluvium, we learn how the older deposit was 
formed over the portion of the Amazon which J had an opportunity 
of examining. In order to describe this we must suppose there was. 
