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 Sourd, 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 



