MEANS OF DISPERSAL. 1 29 



quantities of earth, etc., are sometimes carried away 

 upon the roots of trees by large tropical rivers, where, 

 also, floating rafts or islands, often of considerable size, 

 are frequently formed, and occasionally carried out to 

 sea, to be drifted, perhaps, during calm weather, to great 

 distances. Sir C. Lyell collected some very interesting 

 notes on this subject, which I give in his own words : 



" Within the tropics .... there are floating islets of 

 matted trees, which are often borne along through con- 

 siderable spaces. These are sometimes seen sailing at 

 the distance of fifty or one hundred miles from the 

 mouth of the Ganges, with living trees standing erect 

 upon them. The Amazon, the Congo, and the Orinoco, 

 also produce these verdant rafts, [which are formed of 

 accumulations of floating trees, arrested in their pro- 

 gress by snags, islands, shoals, or other obstructions, 

 as had been] already described when speaking of the 

 great raft of the Atchafalaya, an arm of the Mississippi, 

 where a natural bridge of timber, ten miles long, and 

 more than two hundred yards wide, existed for more 

 than forty years, supporting a luxuriant vegetation, 

 and rising and sinking with the water which flowed 

 beneath it. 



" On these green islets of the Mississippi, observes 

 Malte-Brun, young trees take root, and the pistia and 

 nuphar display their yellow flowers : serpents, birds^ and 

 the cayman alligator, come to repose there, and all are 

 sometimes carried to the sea, and engulphed in its waters. 



" Spix and Martius relate that, during their travels in 

 Brazil, they were exposed to great danger while ascend- 



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