THE ANIMAL KINGDOM. 67 



bed of the sea through their ceaseless development, and by 

 forming large calcareous mountains with their debris ; in 

 fact., when we examine the layers of which these elevations 

 are composed, we perceive that they are formed entirely of 

 corals and bivalves which swarmed in the ancient oceans of 

 the globe. Ground to dust by the furious waves, these crea- 

 tures have only here and there left a few traces* to attest 

 their presence, and serve as a light to the modern investi- 

 gators of science. Such is the opinion of Lyell and most 

 modern geologists. In support of this view it has been ob- 

 served that certain lagoons are filled with a calcareous mud, 

 evidently due to the detritus of the corals, and that so soon 

 as this is dried it exactly resembles the chalk of our an- 

 cient mountains. 



To the action of the waves, the chief agent in trans- 

 forming the coral rocks and bivalves into calcareous strata, 

 there is joined another, much less energetic, it is true, but 

 extremely curious. Mr. Darwin relates that all round the 

 coral islands the transparency of the water allows shoals of 

 fish to be seen, principally of the genus Sparus, which feed 

 on the tips of the branching corals, exactly as flocks of 

 sheep browse on the pasturage of our meadows. In their 

 eagerness to feed on the workman, they devour along with 

 him certain parts of his edifice ; and as these are quite indi- 

 gestible, the result is, according to the English savant, that 

 a part of the chalky substance which encumbers the bottom 

 of the sea in the vicinity of the coral reefs comes from the 

 defecations of these fish. When the Spari are dissected, 

 their alimentary canal is often seen filled with pure chalk. 



The coral islands generally lie on an upheaval of the 



