RATE OF GROWTH OF CORALS. 123 



which sediment is distributed along the coast adjoining and 

 over the sea bottom. 



IV. RATE OF GROWTH OF CORALS. 



The rate of growth of coral is a subject but little under- 

 stood. We do not refer here to the progress of a reef in for- 

 mation, which is another question complicated by many co-op- 

 erating causes ; but simply to the rapidity with which partic- 

 ular living species increase in size. There is no doubt that 

 the rate is different for different species. It is moreover prob- 

 able that it corresponds with the rate of growth of other al- 

 lied polyps that do not secrete lime. The rate of growth of 

 Actiniae might give us an approximation to the rate of growth 

 in coral animals of like size and general character ; for the ad- 

 ditional function of secreting lime would not necessarily re- 

 tard the maturing of the polyp ; and from the Tate of growth 

 of the same animals in the young state, we might perhaps 

 draw some inferences as to the rate in polyps of corresponding 

 size. But no satisfactory observations on this point have yet 

 been made. 



Although the rapidity is undoubtedly far less than was 

 formerly reported, the following facts from different sources 

 seem to show that the rate is greater than has been of late be- 

 lieved. Mr. Darwin, citing from a manuscript by Dr. Allan, 

 of Forres, some experiments made on the east coast of Mada- 

 gascar, states that, in December, 1830, twenty corals were 

 weighed, and then placed by him apart on a sandbank, in three 

 feet water (low tide), and in the July following, each had nearly 

 reached the surface and was quite immovable ; and some had 

 grown over the others Mr. Darwin mentions also a state- 

 ment made to him by Lieut Wellstead, that "in the Persian 



