XXIV 



various countries whose coasts it has visited ; which 

 salts by an eternal increase might otherwise prove as 

 destructive to its inhabitants, as the carbonic acid 

 proves to those on land ; but the Polypi collect, decom- 

 pose, and render them insoluble to the surrounding 

 element which their labours have thus purified ; they 

 unite them in a mass of such extent, that in the 

 course of time the domain of man becomes enlarged, 

 and vegetation blooms and blesses with its fruits on 

 the structures that have ceased to serve them. 



One circumstance worthy to be observed, must not 

 be omitted. To the assistance of Lime we owe the ele- 

 gance and solidity of our buildings, particularly the 

 latter. The calcareous stone, or Carbonate of Lime, 

 that Proteus of the mineral world, is wholly wanting in 

 the Equatorial regions : may we not be allowed to consi- 

 der these Madreporous Polypidoms as destined to sup- 

 ply its absence ? At Djeddah in Arabia, and on many 

 other parts of the Red Sea coast, the houses are con- 

 structed with blocks of beautiful Madrepore. In the 

 Indian Isles, as well as in those of the Eastern Ocean, 

 and in many other parts, the madrepores are used 

 for the manufacture of lime : at Martinique they drag 

 them for that purpose from the bottom of the sea. 



What could we substitute for the Sponges in medi- 

 cine, or for domestic uses ? where should we find a sub- 



