THE OYSTER. 27 



All kinds of shelled molluscs grow more rapidly, and 

 reach a greater size, and have stronger and thicker 

 shells in coral seas, where the supply of lime is un- 

 limited, than in other waters. In some parts of the 

 Bahamas the large pink-lipped conch, the one which 

 we often see for sale in the fruit stores of Baltimore, 

 is so abundant that whole islands, large enough to be 

 inhabited, are entirely made up of the broken frag- 

 ments of these beautiful shells, which have been 

 pounded to pieces and heaped up by the waves. 



The fresh-water mussels of our western rivers are 

 very large in limestone regions, and so abundant that 

 the bottom is almost paved with them, while in another 

 river, perhaps only a few miles away, but flowing 

 through a country where there is little lime, they are 

 few and very small, with thin, fragile shells. 



If you turn over the old bones which are sometimes 

 found in the woods and fields, you will nearly always 

 find a number of snails which have been drawn to 

 them for the sake of the lime. 



In order that the oyster may grow rapidly, and may 

 be securely protected from its enemies, it must have 

 lime. The lime in the water of the bay is derived in 

 great part from the springs of the interior, which, flow- 

 ing through limestone regions, carry some of it away 

 in solution, and finally carry it down the rivers and 

 into the bay. Some of it is no doubt derived from 

 deposits of rock in the bed of the ocean, and some from 

 the soil along the shores. The geologist tells us that 

 the limestone rock has all of it at one time been part 



