November 28, 1884.1 



SCIENCE. 



491 



All through this region the porordca 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 comparatively shallow places 

 make it much more so, and fill it with all the 

 sediment it can possible cany. Even when I 

 entered the Araguary, a time when there was 

 the least possible tidal disturbance, the water 

 near the mouth of this stream was so muddy, 

 that a thick sediment would settle in the bot- 

 tom of a vessel of it left standing a single 

 minute ; though the water of the Aragua^ 

 proper, as far down as the Veados, is of a clear, 



SHORE 2 M. HIGH, WASHED BY THE POROR(5CA, FORMERLY 

 COVERED WITH FOREST. 



dark color. But the work of tearing down and 

 that of building up are 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 main- 

 land, and promontories built out. To the north- 

 west of Faustinho is an island known as the 

 Una 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 a little taller, and so on ; so that 

 the vegetation sloped upward and back to a 

 forest from twenty to thirty metres high in the 

 middle of the island. 1 Again : on the southern 

 side of the mouth of the Araguary was a point 

 of land nearly or quite six miles in length, and 

 covered with vegetation, from young shoots to 

 bushes six metres high. I was told, that, one 

 year before, this was nothing more than a sand- 

 bar, without a sign of vegetation on it. The 

 western end of the Island of Porquinhos was 

 once known as Ilha Franco ; but the channel 

 that separated it from the Porquinhos has been 

 filled up gradually, and the two islands are now 

 one, though the upper end of it is still known 

 as Franco. The point in the mouth of the 

 Araguary known as the Ilha dos Veados (' deer 

 island') was, at the time of my visit, fast being 

 joined to the mainland. A couple of }-ears 



1 The plants growing upon this newly formed land are all of 

 one kind. They are called Ciriuba, or Xiriuba, by the inhabit- 

 ants, and belong to the family Verbenaceae, genus Avicennia. 



before, boats navigating the Araguary passed 

 through the channel on the south side of the 

 island. In 1881 it was no longer navigable, 

 and the Veados was rapidly being made part 

 of the right bank of the river. 



Owing to this shifting of material, the pilots 

 never know where to find the entrance to the 

 Araguary River. One week the channel may 

 be two fathoms deep on the north side, and 

 the next it may be in the middle ; or it may 

 have disappeared altogether, leaving the river- 

 bed perfectly flat, with only one fathom of 

 water across the whole mouth. The bar was 

 in this last-mentioned condition when I passed 

 over it in 1881. At this time another bar ex- 

 tended eastward from the eastern end of Bai- 

 lique; while a little farther out was another 

 just south of the same line, as I have indicated 

 on the map. The shifting nature of the sand- 

 bars about the mouth of the Araguary renders 

 it unsafe for vessels drawing more than one 

 fathom to enter this river, except at high tides. 

 But, as high tides and the porordca come at 

 the same time, only light-draught steamers can 

 enter by waiting well outside the bar until the 

 force of the porordca is spent. 



With the few canoes or small sailing-vessels 

 that enter this stream (probably less than 

 half a dozen a year) , it is the custom to come 

 down past Bailique with the outgoing tide, and 

 to anchor north of the bar that projects from 

 the southern side of the Araguary, and there 

 to await the turn of the tide to ascend the lat- 

 ter river. Care is always taken to pass this 

 point when the tides are least perceptible. 



Although the porordca breaks as far up the 

 Araguary as midway between the Veados and 

 the entrance to the Apureminho, its violence 

 seems to be checked by the narrowing of the 

 stream below the Veados, b} T the turns in the 

 river, and by the vegetation along the banks. 



This vegetation is of the kind against which 

 it seems to be least effective, namely, bamboos. 

 The} 7 grow next the stream from near the mouth 

 to the foot of the falls above the colony, and 

 form a fringe to the heavy, majestic forest be- 

 hind them, than which nothing could be more 

 strikingly beautiful. The clusters next the 

 stream droop over till their graceful plumes 

 touch the surface of the water; and, as the 

 plants grow older, the}' droop lower, until the 

 stream is filled with a yielding mesh of canes. 

 I measured a number of these bamboos ; and 

 the longer ones, taken at random, were from 

 twent}* to twent}'-five metres in length, and 

 from seven to ten centimetres in diameter. A 

 more effectual protection against the porordca 

 could hardly be devised. 



