124 CORALS AND CORAL ISLANDS. 
Gulf a ship had her copper bottom encrusted in the course of 
twenty months, with a layer of coral two feet thick,—evi- 
dently to be accepted hesitatingly. He also speaks of a chan- 
nel in the lagoon of Keeling atoll having been stopped up in 
less than ten years; and of the natives of the Maldives find- 
ing it necessary occasionally to root out, as they express it, 
coral knolls from their harbors. 
Mr. Stutchbury describes a specimen consisting of a spe- 
cies of oyster whose age could not be over two years, encrust- 
ed 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. Weinland states that on Hayti, in a small coral 
basin between the town of Corail and the island Caymites, 
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 
growth of three to five inches, above referred to, might. have 
been made during the three winter months. 
Duchassaing (in L’Institut, 1846, p. 117) observes that in 
two months some large individuals of Madrepora prolifera 
which he broke away, were restored to their original size. 
More definite and valuable is the observation of Mr. L. F. de 
Pourtales, that a specimen of Meandrina labyrinthica, meas: 
uring a foot in diameter, and four inches thick in the most 
convex part, was taken from a block of concrete at Fort Jet: 
terson, Tortugas, which had been in the water only twenty 
