328 J. STANLEY GARDINER. 



more it is to the rate of growth of the corals that we must look to get an idea of the 

 possible and probable rates of the reef itself 



An almost insuperable difficulty for the consideration of our problem lies in the necessity 

 of determining the rate of growth of the corals at different depths. There are no fixed 

 laws for different species or even genera, but the rate is mainly affected in every case by 

 the environment. When reef corals have once fairly fixed themselves on a shoal, the task 

 of determining when that shoal will reach the surface, is as nothing compared to the difficulty 

 of ascertaining the time that has been taken by the coral larvae to so secure themselves. 

 The larvae must have a firm support, must in fact build up their houses on rocks, and it 

 is owing to this that the growth of new shoals in lagoons is so rare. Above I only deal 

 with reef corals; the task is many times magnified when we come to consider other forms. 

 The problem, in truth, is one beset with innumerable difficulties, but one of such importance 

 that any results, however small, are of great interest and value. 



The facts relating to the growth of corals and reefs up to the year 1890 were ably 

 summarised by Dana^ whose conclusions are best expressed in his own words : — " Whatever 

 the uncertainties it is evident that a reef increases in height or extent vpith extreme slo^vness. 

 If the rate of upward progress is one-sixteenth of an inch a year, it would take for the 

 addition of a single foot to its height, one hundred and ninety years, and for jive feet 

 a thousand years." (The italics are Dana's, not mine.) This was published antecedent to the 

 appearance of Murray's full work on the influence of pelagic oi-ganisms on the formation of 

 rock -, and it is evident that the possibilities of the enormous rate of increase of these and 

 other organisms were not understood by Dana. Unfortunately I am unable to admit much 

 of Dana's premiss, as I differ profoundly from him in regard to the structure of coral reefs 

 and the mode of growth they exhibit at the present day. 



Little work has been published on the subject since Dana's resume. Agassiz gave a few 

 photographs of the natural sizes of certain corals from a telegraph cable at a depth of 

 6 — 7 fathomsl Taking the measurements from the figures of the specimens, these show 

 a maximum upward rate of growth of respectively 3^, 2 and 3 inches, and lateral extensions 

 of 3^, If and 2\ inches, taking the halves of the total breadth of each, in seven years. 

 More recently I discussed the rate of growth of certain specimens from Fiji^, but with no 

 attempt to deduce general conclusions as to the rate of reefs. Calculated out on Dana's 

 method and remembering that practically the whole surface of a reef is covered with growing 

 corals, the Fijian specimens would give an average rate of upward progress of 5'19 mm. in 

 one year or a thickness of about 17 feet in 1000 years. 



Many of the inhabited islands of the Maldives have definite channels for theii- small 

 fishing and trading boats, excavated through their encircling reefs, even the shallowest usually 

 with at least 4 feet of water at low tide. The boat channels between the land and reef 

 accordingly make safe harbours for small vessels, and slips on the shores serve for repairing 

 the latter. These canals, or magu — a naturally formed ship's passage, such as those into any 

 of the lagoons, is termed in Maldivian kandu — by the laws and customs of the country are 

 cleared out according to the needs of the different districts once every 2 to 5 years. In 

 Mahlos, Male and atolls more particularly under the sway of the Sultan, the law is that this 



1 Coral and Coral Island.^, 1890, pp. 123— 127, 253—2.58, ■' Bull. Mas. Comp. Zonl. vol. xx. p. 61 (IS'.IO). 



and 396-397. * Proc. Camb. Phil. Soc. vol. xi. pt. iii. pp. 214—219 



2 "Deep-Sea Deposits," Challenger Reports, 1891. (1901). 



