Chap. III. 
FALLING BANKS. 
171 
fish, and so forth, has suggested itself to me. Their 
rounded, water- worn appearance showed that they must 
have been rolled about for a long time in the shallow 
streams near the sources of the rivers at the feet of the 
volcanoes, before they leapt the waterfalls and embarked 
on the currents which lead direct for the Amazons. 
They may have been originally cast on the land and 
afterwards carried to the rivers by freshets ; in which 
case the eggs and seeds of land insects and plants might 
be accidentally introduced and safely enclosed with 
particles of earth in their cavities. As the speed of the 
current in the rainy season has been observed to be 
from three to five miles an hour, they might travel an 
immense distance before the eggs or seeds were 
destroyed. I am ashamed to say that I neglected the 
opportunity, whilst on the spot, of ascertaining whether 
this was actually the case. The attention of Naturalists 
has only lately been turned to the important subject of 
occasional means of wide dissemination of species of 
animals and plants. Unless such be shown to exist, it 
is impossible to solve some of the most difficult problems 
connected with the distribution of plants and animals. 
Some species, with most limited powers of locomotion, 
are found in opposite parts of the earth, without existing 
in the intermediate regions ; unless it can be shown 
that these may have migrated or been accidentally trans- 
ported from one point to the other, we shall have to 
come to the strange conclusion that the same species 
had been created in two separate districts. 
Canoemen on the Upper Amazons live in constant 
