200PHYTES. 25 



able. One on the east coast of New Holland is known to be 

 nearly 1000 miles in length, and unbroken for a distance of 

 350 miles. Some groups in the Pacific are 1100 to 1200 in 

 length, by 350 to 400 in breadth, and these are not formed in 

 an expanse of deep and tranquil waters, but in the midst of 

 an ocean which is ever breaking upon the barrier which the 

 little architects are silently building in the midst of its uproar. 



"The ocean," says Mr. Darwin, " throwing its breakers on 

 these outer shores, appear an invincible enemy ; yet we see it 

 resisted, and even conquered, by means which seem at first 

 most weak and inefficient. No periods of repose are granted, 

 and the long swell caused by the steady action of the trade- 

 wind never ceases. The breakers exceed in violence those of 

 our temperate regions; and it is impossible to behold them 

 without feeling a conviction that rocks of granite or quartz 

 would ultimately yield and be demolished by such irresistible 

 forces. Yet these low, insignificant coral islets stand, and are 

 victorious; for here another power, as antagonist to the 

 former, takes part in the contest. The organic forces separate 

 the atoms of carbonate of lime one by one from the foaming 

 breakers, and unite them into a symmetrical structure; myriads 

 of architects are at work day and night, month after month, 

 and we see their soft and gelatinous bodies, through the 

 agency of the vital laws, conquering the great mechanical 

 power of the waves of an ocean which neither the art of man 

 nor the inanimate works of Nature could successfully resist." 



It was formerly supposed that the coral-building polypes 

 worked in unfathomable depths, and in the course of ages 

 reared their pile to the surface of the water; and it was also 

 conjectured that the oval or circular form of the Lagoon islands 

 might be caused by their being based upon the craters of ex- 

 tinct submarine volcanoes. Both these hypotheses are now 

 abandoned. Recent and widely-extended observations have 

 led to the conclusion that all the phenomena attending the 

 growth and structure of coral reefs may be explained by 

 reference to the combined operation of three causes: 



1st, 'That the species of polypes most efficient as coral- 

 builders, work only at limited depths, not exceeding twenty 

 or thirty fathoms.* 



* This may seem at variance with the fact, that in the immediate 

 vicinity of some of the Coral islands, the sea is of great, and 'sometimes 

 of unfathomable depth. But if, according to Mr. Darwin's theory, the 



