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- 
