THE "POROROCA," OR BORE, OF THE AMAZON. 211 



away ; but all this is the work of a rapid current, for the surf of 

 the pororoca does not reach Macapd,. Moreover, there is a marked 

 difference in character between the washing done by the pororoca 

 and that done by the ordinary river or tide current. The latter 

 works from below, and, by undermining and softening the bank, 

 causes what is known through the Amazon Valley as terras calii- 

 das, or fallen banks. The land falls into the stream in sections of 

 various widths, and not infrequently these form temporary ter- 

 races miles in length. These terras caliidas are most common 

 and most extensive on the upper Amazon during high water ; but 

 they may be seen on a small scale at various places through the 

 valley.* From this it is clear that the work of destruction goes 

 on entirely below the surface. With the pororoca, on the con- 

 trary, the water is dashed fairly against the banks, the earth 

 is washed away from above as well as from below, and the shore 

 is left clear of loose debris. The depth to which the banks are 

 cut shows that this disturbance is also a profound one ; so much 

 so, indeed, that on the northwest side of Porquinhos the deepest 

 place in the channel of the river was, in 1881, close to this island, 

 where the action of the pororoca was most violent. 



Throughout this region of the Araguary the pororoca is largely 

 instrumental in the rapid and marked changes that are constantly 

 going on. The water of the Amazon is notoriously muddy, and, 

 as would naturally be expected, these disturbances in compara- 

 tively shallow places make it much more so, and fill it with all 

 the sediment it can possibly carry. Even when I entered the 

 Araguary, a time when there was the least possible tidal disturb- 

 ance, the water near the mouth of this stream was so muddy 

 that a thick sediment would settle in the bottom of a vessel of it 

 left standing a single minute ; though the water of the Araguary 

 proper, as far down as the Veados, is of a clear, dark color. But 

 the work of tearing down and that of building up is equally rapid, 

 and the vegetable world takes quick possession of what the sea 

 offers it ; and, while some islands are being torn away, others are 

 being built up, old channels being filled, islands joined to the 

 mainland, and promontories built out. To the northwest of Faus- 

 tinho is an island known as the Ilha Nova (New Island), about ten 

 miles long by about three wide, when I saw it, and which, I was 

 assured by several trustworthy persons, did not exist six years 

 before. In 1881 it was covered by a dense forest. The young 

 plants were sprouting at the water's edge, those behind were a 

 little taller, and so on ; so that the vegetation sloped upward and 

 backward to a forest from twenty to thirty metres high in the 



* For a good description of the terras cahidas, see The Naturalist on the Amazon, by 

 Bates, fifth edition, p. 249. 



