768 C. B. BROWN ON THE ANCIENT 
The latter rested upon the eroded surface of the bluish, arena- 
ceous, laminated clay, which dipped to the west, and enclosed a thick 
layer of yellowish sand, containing lines of clay ironstone. 
Two sections taken at Tonantins were as follows :— 
ft. 
(i 10 Red loam. 
i 4 40 Yellow sand, with layer of gravel near its base. 
5 Yellow sand, with layers of iron-clay in irregular folds. 
| 20 Pink and white banded clay of fine texture. 
( 10 Red sand and loan. 
| 35 Yellow sand. 
If. 4 20 Banded red and grey clay. 
! Blue laminated clay, qiseins thin layers of sand between the 
| 2 2 lamin, and containing imbedded leaves. 
\ Yellow laminated clay. 
In one part white sand took the place of the yellow sand; while 
in another the bluish, laminated, micaceous clay made its appear- 
ance, dipping west at a low angle. Upon its denuded surface rests 
the iron-oxide layer, along with yellow ochreous clay in yellow sand, 
with pink clay and sand above. The fine, soft, yellow ochreous clay 
is used by the natives as a pigment. 
About one mile below St. Paulo we have as follows :— 
10 feet of reddish arenaceous loam. 
15 ,, white sand, containing pebbles. 
These rest upon bluish-grey clay beds, which I consider to be of 
Tertiary age. 
At Caldeirad the section is a tolerably clear one, and is as 
follows :— 
ft. in. 
1 6 Red loam. 
12 0 Grey and motiled clay. 
11 O Reddish sand. 
12 0 Yellowish speckled sand. - 
2 O Blue clay. 
0 Grey sand. 
Blue clay. 
Grey sand. 
5 O Blue clay. 
10 O Yellowish and grey sand, stained with iron oxide. 
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Having now given the details of a number of the principal cliff- 
sections on the main river, I will proceed to describe a few of those 
occurring on its tributaries, so as to show the composition of the de- 
posit in both northerly and southerly directions. 
The Trombetas does not afford any good section, as the deposit 
does not extend far up it. At Urua-tapera Point, however, there is 
a cliff 90 feet high, composed of red and purplish sand beds of the 
river-deposit, resting upon an older formation of red shale. 
On the upper part of the Rio Negro there are beds of the river- 
deposit which have been laid down by the Negro itself. The first 
set of cliffs above Caburie shows grey and mottled clay, resting upon 
yellowish and grey false-bedded sand. In the third set of cliffs there 
are but few sand beds, and the whole front is made up of clay beds. 
