38 THE DISPERSAL OF SHELLS. . 



them out to sea. Some such trees might drift into bays 

 at the mouths of rivers in other countries^ and I have 

 seen just such floating in the mouths of the Manatee 

 and Caloosahatchee Rivers in Florida. It must be 

 remembered that all these rivers, during the rainy 

 season, are only very slightly brackish, or even entirely 

 fresh, throughout their estuary portions. 



" Trees carried into such places^ and bearing fresh- 

 water shells, might be driven up and landed by tide and 

 winds, and a colony of living inhabitants established. 

 Many of the shallow bays along the coast of Florida 

 become perfectly fresh during the rainy season, as some 

 five feet of water falls there in three months, and the 

 same thing no doubt occurs in other parts of the tro[)ics 

 where the rain-fall is much greater. In Florida these 

 bays at such times connect with ponds of water on the 

 flat lands, so that often for miles the whole country 

 from the shore far inland is nearly covered with fresh 

 water. 



" At the south-western extremity of the State are found 

 the Ten Thousand Islands, an innumerable group 

 scattered over a space of a hundred and fifty miles of 

 coast separated by brackish channels through which the 

 tide flows in and out, gradually becoming entirely fresh 

 in the region of the Everglades. So there would be no 

 trouble about landing a colony of fresh-water snails on 

 the Florida coast, and the only difficulty would be in 

 bringing them across. Could they stand the drying 

 and the salt water of the ocean > " 



[After showing that many kinds are able to live for a 



