FALLING BANKS 



349 



below Monte Alegre, about 900 miles further down the 

 river : having reached this distance, pumice-stones would 

 be pretty sure of being carried out to sea, and floated 

 thence with the north-westerly Atlantic current to shores 

 many thousand miles distant from the volcanoes which 

 ejected them. They are sometimes found stranded on 

 the banks in different parts of the river. Reflecting on 

 this circumstance since I arrived in England, the proba- 

 bility of these porous fragments serving as vehicles for 

 the transportation of seeds of plants, eggs of insects, 

 spawn of fresh-water 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 Ama- 

 zons. 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 dis- 

 tance 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. Un- 

 less such be shown to exist, it is impossible to solve some 

 of the most difficult problems connected with the distribu- 

 tion 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 transported 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. 



Canoe -men on the Upper Amazons live in constant 

 dread of the * terras cahidas or landslips, which occasion- 

 ally take place along the steep, earthy banks ; especially 

 when the waters are rising. Large vessels are sometimes 

 overwhelmed by these avalanches of earth and trees. I 



