CAVITIES Ilf THE SOCK. 
263 
existence of subterraneous cavities in tbe yellalas or rapids 
of the river Congo was discovered. The pongo of Manse- 
riche, which ought rather to be called a strait than a fall, 
ingulfs, in a manner not yet sufficiently explored, a part of 
the waters and all the floating wood of the Upper Marahon. 
The spectator, seated on the bank of the Orinoco, with 
his eyes fixed on thoso rocky dikes, is naturally led to 
inquire whether, in the lapse of ages, the falls change their 
form or height. I am not much inclined to believe in such 
effects of the shock of water against blocks of granite, and 
in the erosion of siliceous matter. The holes narrowed 
toward the bottom, the funnels that are discovered in the 
r audnles, as well as near so many other cascades in Europe, 
are owing only to the friction of the sand, and the move- 
ment of quartz pebbles. We saw many such, whirled per- 
petually by the current at the bottom of the funnels, and 
contributing to enlarge them in every direction. The 
ponyos of the river Amazon are easily destroyed, because 
the rocky dikes are not granite, but a conglomerate, or red 
sandstone with large fragments. A part of the pongo of 
nentema was broken down eighty years ago, and the course 
°f the waters being interrupted by a new bar, the bed of 
the river remained dry for some hours, to the great astonish- 
ment of the inhabitants of the village of Payaya, seven 
leagues below the pongo. The Indians of Atures assert 
(and in this their testimony is contrary to the opinion of 
Caulin) that the rocks of the raudal preserve the same 
a ?pect ; but that the partial torrents into which the great 
fiver divides itself as it passes through the heaped blocks 
°f granite, change their direction, and carry sometimes 
m°re, sometimes less water towards one or the other bank ; 
jmt the causes of these changes may be very remote from 
’me cataracts, for in the rivers that spread life over the 
surface of the globe, as in the arteries by which it is 
diffused through organized bodies, all the movements are 
Propagated to great distances. Oseilhitious, that at first 
®eetn partial, react on the whole liquid mass contained in 
’me trunk as well as in its numerous ramifications. 
Some of the Missionaries in their writings have alleged 
the inhabitants of Atures and Maypures have been 
s truck with deafness by the noise of the Great Cataracts 
