90 LECTURE VH. 



of four hundred miles, and another which runs 

 along the north-east coast of Australia one 

 thousand miles in extent. Now, supposing this 

 latter to be only a quarter of a mile in breadth 

 and one hundred and fifty feet deep, here is a work 

 compared with which the walls of Babylon, the 

 Great Wall of China, or the Pyramids of Egypt, 

 may be called children's toys. You must recol- 

 lect also that the operations of the coral insect 

 were carried on amidst the waves of the ocean, 

 and in defiance of its storms, which, as you know, 

 often sweep away the solid works of man. 



Such are some of the operations of that extra- 

 ordinary insect, the coral ; and I have pointed 

 out their influence on the caustic lime which 

 finds its way into the sea, and which is so inju- 

 rious to animal life. But there are other means 

 provided for neutralizing and rendering the lime 

 harmless. Sponges, sea-flowers of various de- 

 scriptions and in innumerable quantities, and 

 other marine animals, all having life, act as 

 agents in this wise arrangement of Providence 

 to purify the waters of the ocean. Sponges, you 

 might suppose, have no vitality or living organs ; 

 but this is not the case, although they perhaps 

 are the lowest in the scale of living beings, as I 



