434 A JOURNEY IN BRAZIL. 
serve as a geological section, so perfectly does it display 
the three characteristic Amazonian formations above de- 
scribed. At its mouth, near the town of Soure, and at Sal- 
vaterra, on the opposite bank, may be seen, lowest, the well- 
stratified sandstone, with the finely laminated clays resting 
upon it, overtopped by a crust ; then the cross-stratified, 
highly ferruginous sandstone, with quartz pebbles here and 
there ; and, above all, the well-known ochraceous, unstrati- 
fied sandy clay, spreading over the undulating surface of 
the denudated sandstone, following all its inequalities, and 
filling all its depressions and furrows. But while the Iga- 
rape Grande has dug its channel down to the sea, cutting 
these formations, as I ascertained, to a depth of twenty-five 
fathoms, it has thus opened the way for the encroachments 
of the tides, and the ocean is now, in its turn, gaining upon 
the land. Were there no other evidence of the action of the 
tides in this locality, the steep cut of the Igarape Grande, 
contrasting with the gentle slope of the banks near its mouth, 
wherever they have been modified by the invasion of the sea, 
would enable us to distinguish the work of the river from 
that of the ocean, and to prove that the denudation now go- 
ing on is due in part to both. But besides this, I was so 
fortunate as to discover, on my recent excursion, unmistak- 
able and perfectly convincing evidence of the onward move- 
ment of the sea. At the mouth of the Igarape Grande, both 
at Soure and at Salvaterra, on the southern side of the Iga- 
rape, is a submerged forest. Evidently this forest grew in 
one of those marshy lands constantly inundated, for between 
the stumps is accumulated the loose, felt-like peat character- 
istic of such grounds, and containing about as much mud 
as vegetable matter. Such a marshy forest, with the stumps 
of the trees still standing erect in the peat, has been laid 
