218 
PHYSICAL HISTORY OF THE 
emptying almost immediately into the sea, 
would ask themselves whether it had ever 
been indeed a branch of the Amazons, just as 
they now question whether the Tocantins is 
a tributary of the main stream or an indepen¬ 
dent river. But to return to Marajo, and to 
the facts actually in our possession. 
The island is intersected, in its southeast¬ 
ern end, by a considerable river called the 
Igarap6 Grande. The cut made through the 
land by this stream seems intended to serve 
as a geological section, so perfectly does it 
display the three characteristic Amazonian 
formations above described. At its mouth, 
near the town of Sour6 and at Salvaterra, on 
the opposite bank, may be seen, lowest, the 
well-stratified sandstone with the finely lami¬ 
nated clays resting upon it, overtopped by a 
crust; then the cross-stratified, highly ferru¬ 
ginous sandstone, with quartz pebbles here and 
there; and, above all, the well-known ochra- 
ceous, unstratified sandy clay, spreading over 
the undulating surface of the denudated sand¬ 
stone, following all its inequalities, and filling 
all its depressions and furrows. But while the 
Igarape Grande has dug its channel down to 
