zoornTTES. 25 



markable. 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, appears an invincible enemy; yet we 

 see it resisted, and even conquered, by means which seem 

 at first most weak and inefiicient. 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 impos- 

 sible to behold them without fueling a conviction that 

 rocks of granite or quartz would ultimately yield and be 

 demolished by such irresistible forces. Yet these low, in- 

 significant 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 

 islandsmightbecaused by their being based upon the craters 

 of extinct 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 e.xplained 

 by reference to the combined operation of three causes : — 



1st, — That the species of polypes most efiicient 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 tae Coral islands, the sea is of gieat, and sometimes 



