36 THE OTSTEE. 



a stratum of about two feet in tliickness. But the 

 largest fossil oyster banks are those raised by earth- 

 quakes along the western shores of South America, 

 which measure from sixty to eighty feet in depth, are 

 often forty miles in length, and in many places stretch 

 above two miles into the interior. 



The Abbe Dicquemare, fond of trying experiments in 

 the spread of gastronomy, even to the stewing a mess of 

 Gemmacece, the Gems of our water- vivaries, till they had 

 something of the flavour of oysters, asserts that, when 

 in a state of liberty, oysters can move from one place 

 to another by suddenly admitting sea water into the 

 shell, which they are able to open and shut with extra- 

 ordinary power and rapidity, whereby they produce a 

 strange sound ; and this observation has been confirmed 

 by other natui'alists, and is recorded as an ascertained 

 fact in several books of natural science. In like manner 

 they defend themselves against smaller animals, especially 

 against the spider crab, which constantly tries to pene- 

 trate into their half open shells. Much natural instinct 

 or foresight is also attributed to the oyster ; in proof of 

 which I may name that, when in a position which is 

 exposed to the variations of the tide, oysters seem to be 

 aware that they remain for some hours without water, 

 and consequently provide it within their shells. 



This makes such oysters far more fit to be conveyed 

 to a distance, than those taken nearer to the shore, which 

 evacuate the water, thus exposing themselves to the heat 

 of the sun, the cold, or an attack from their enemies ; 

 and this, too, is the reason why Colchester or Pyfleet 

 oysters, packed at the beds, are in such request. 



