VALLEY OF THE AMAZONS. 
219 
the sea, cutting these formations, as I ascer¬ 
tained, to a depth of twenty-five fathoms, it 
has thus opened the way for the encroach¬ 
ments 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 Igarap4 
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 going on is due in part to 
both. But besides this, I was so fortunate as 
to discover here unmistakable and perfectly 
convincing evidence of the onward movement 
of the sea. At the mouth of the Igarap6 
Grande, both at Soure and at Salvaterra, on 
the southern side of the Igarape, is a sub¬ 
merged forest. Evidently this forest grew in 
one of those marshy lands constantly inun¬ 
dated, for between the stumps is accumulated 
the loose, felt-like peat characteristic of such 
grounds, and containing about as much mud 
as vegetable matter. Such a marshy forest, 
with the stumps of the trees still standing 
