CORAL-REEFS. 103 



polypifers can exist. If it be asked, at what rate in years I 

 suppose a reef of coral favourably circumstanced could 

 grow up from a given depth ; I should answer, that we 

 have no precise evidence on this point, and comparatively 

 little concern with it. We see, in innumerable points over 

 wide areas, that the rate has been sufficient, either to bring 

 up the reefs from various depths to the surface, or, as is 

 more probable, to keep them at the surface, during pro- 

 gressive subsidences ; and this is a much more important 

 standard of comparison than any cycle of years. 



It may, however, be inferred from the following facts, that 

 the rate in years under favourable circumstances would 

 be very far from slow. Dr. Allan, of Forres, has, in his 

 MS. Thesis deposited in the library of the Edinburgh 

 University (extracts from which I owe to the kindness 

 of Dr. Malcolmson), the following account of some experi- 

 ments, which he tried during his travels in the years 1830 to 

 1832 on the east coast of Madagascar. "To ascertain the 

 rise and progress of the coral-family, and fix the number of 

 species met with at Foul Point (lat. 17 40'), twenty species 

 of coral were taken off the reef and planted apart on a 

 sand-bank three feet deep at low water. Each portion 

 weighed ten pounds, and was kept in its place by stakes. 

 Similar quantities were placed in a clump and secured as the 

 rest. This was done in December 1830. In July follow- 

 ing, each detached mass was nearly level with the sea at 

 low water, quite immovable, and several feet long, stretch- 

 ing as the parent reef, with the coast current from north to 

 south. The masses accumulated in a clump were found 

 equally increased, but some of the species in such unequal 

 ratios, as to be growing over each other." The loss of 

 Dr. Allan's magnificent collection by shipwreck, unfortu- 

 nately prevents its being known to what genera these corals 



