HALF AN HOUR WITH SHELL-FISH (BIVALVES). 205 



XII. 



HALF AN HOUE WITH SHELL-FISH (BIVALVES). 



THE enormous fertility of marine mollusca can only 

 be understood when we are thoroughly acquainted 

 with the claims made upon them. They are caught 

 in hundreds of millions every year, as cockles, 

 mussels, oysters, &c., to be consumed by man. On 

 many parts of our coasts, the mussel-beds are worked 

 for the purpose of manuring the half-barren lands, 

 and thousands of cartloads are carried off for this 

 purpose. The bivalves, especially, furnish the prin- 

 cipal food of the carnivorous univalve molluscs, and 

 their perforated shells, thrown ashore, only too 

 surely indicate the end that overtook them. The 

 star-fishes fill their greedy maws with these 

 dainties ; fishes of many species find in them their 

 staple food. And yet, in spite of these immense 

 demands and ravages, the ocean bed is being covered 

 in many places with calcareous deposits formed by 

 the accumulation of dead shells, &c. The supply is 

 much greater than the demand, and the excess is 

 being utilised in laying the probable foundations for 

 future continents. 



This remark suggests to us the work done by 

 certain lowly-organised molluscs in forming the 

 actual solid land on which we live. In Derbyshire, 



