RATE OF GROWTH OF CORALS. 97 



{)erhaps draw some inferences as to the rate in polyps of cor- 

 responding 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 

 believed. 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 statement made to him by Lieutenant Wellstead, that 

 *'in the Persian Gulf a ship had her copper bottom in- 

 crusted in the course of twenty months, with a layer ot 

 coral two feet thick," — evidently to be accepted hesitatingly. 

 He also speaks of a channel in the lagoon of Keeling 

 atoll having been stopped up in less than ten years ; and 

 of the natives of the Maldives finding it necessary oc- 

 casionally to root out, as they express it, coral knolls from 

 their harbours. 



Mr. Stutchbury describes a specimen consisting of a spe- 

 cies of oyster whose age could not be over two years, in- 

 crusted by an Agaricia weighing two pounds nine ounces ; 

 but he does not state whether the shell was that of a living 

 oyster or not. 



Dr. D. F. VVeinland states that on Hayti, in a small coral 

 basin between the town of Corail and the island Cay mites, 

 never disturbed by vessels on account of the small depth of 

 water, he observed several branches of the Madrepora cervi- 

 cornis projecting above the surface of the water from three to 

 five inches, all of which, down to the water level, were dead, 

 as a result evidently of exposure to the air. This was in the 

 month of June. He adds that all along the north shore of 

 Hayti, the water level is from four to six feet higher in the 

 winter season than during summer ; and suggests that the 



H 



