TINY ROCK-BUILDERS. 159 



coral growth may have started on a platform of 

 volcanic origin. A volcanic cone may have been 

 worn down to the necessary depth by the action of 

 the waves, or raised to the required height by the 

 continued deposition upon it of the shells and 

 remains of dead marine animals. When the cone, or 

 the base, had acquired the proper depth, the polypes 

 brought to it would begin their operations, building 

 upwards and outwards the inner portion, or lagoon, 

 being gradually deepened by the solvent action of 

 the sea-water. The advantage of this theory is, that 

 it applies to areas which are being elevated as well as 

 to stationary or subsiding regions ; and there seems 

 to be more evidence of elevation than of subsidence 

 in coral areas. It also explains the curious fact 

 that reefs expand laterally by the more rapid growth 

 on the seaward side, while they remain always only 

 a few hundred yards wide the inner lagoons be- 

 coming larger and deeper as the result of the 

 solvent action of the carbonic acid of the sea-water 

 upon the calcareous elements of the coral structure. 

 These theories of Darwin and Murray are still 

 being discussed. Not long since, in the Nineteenth 

 Century, a formidable attack was made by the Duke 

 of Argyll, not only on Darwin's hypothesis of coral 

 formation, but also on scientific men in general, for 

 what he described as " a great conspiracy " on their 

 part in ignoring Murray and still clinging to Darwin's 

 early explanation. He went so far as to say that, 

 " with all his conscientiousness, with all his caution, 

 with all his powers of observation, Darwin, in this 

 matter, fell into errors as profound as the abysses of 



