TINY ROCK-BUILDERS. 157 



bonate of lime which they are continually secreting 

 from the water of the ocean, the mind cannot fail to 

 be filled with astonishment. 



" Millions of millions thus, from age to age, 

 With simplest skill, and toil unweariable, 

 No moment and no movement unimproved, 

 Laid line on line, on terrace terrace spread, 

 To swell the heightening, brightening, gradual mound, 

 By marvellous structure climbing towards the day 

 Each wrought alone, yet all together wrought ; 

 Unconscious, not unworthy, instruments, 

 By which a Hand invisible was rearing 

 A new creation in the secret deep. 

 Omnipotence wrought in them, with them, by them, 

 Hence what Omnipotence alone could do 

 Worms did." 



Formerly it was imagined that these coral struc- 

 tures had been built up from the bed of the sea, 

 and consequently it was predicted that gradually 

 the mighty Pacific would be divided by a vast 

 tropical zone of coral rock, but later on it was 

 ascertained that the polypes cannot live at a greater 

 depth than about twenty to thirty fathoms. Mr. 

 Darwin's well-known treatise on Coral Reefs contains 

 an explanation of the various phenomena concerned 

 which has been universally accepted up to our own 

 day. He supposed that after the polypes commenced 

 to build around the shelving sides of an island at 

 some depth below the surface, the bed of the sea 

 began to subside, the rate of upward growth of the 

 polypes keeping pace with the sinking of the ocean 

 floor. According to this theory, a fringing reef would 

 first be formed rising to within a few fathoms of the 



