106 
RATE OF GROWTH. 
Cn. IV. 
different kinds of coral, when placed in one clump, 
having increased in extremely unequal ratios, is very 
interesting, as it shows the manner in which a reef, 
supporting many species of coral, would probably be 
affected by a change in the external conditions 
favouring one kind more than another. The growth 
of the masses of coral in N. and S. lines parallel to 
the prevailing currents, whether due to the drift- 
ing of sediment or to the simple movement of the 
water, is, also, an interesting circumstance. 
Lieut. Wellstead, I.N., informed me that in the 
Persian Gulf a ship had her copper bottom en- 
crusted in the course of twenty months with a layer 
of coral two feet in thickness, which it required great 
force to remove when the vessel was docked : it was 
not ascertained to what order this coral belonged . 1 
1 Mr. Stutchbury (West of England Journal, No. I. p. 50) bas 
described a specimen of Agaricia, ‘ weighing 2 lbs. 9 oz., which sur- 
rounds a species of oyster, whose age could not be more than two 
years, and yet is completely enveloped by this dense coral.’ I pre- 
sume that the oyster was living when the specimen was procured ; 
otherwise the fact tells nothing. Mr. Stutchbury also mentions an 
anchor, which had become entirely encrusted with coral in fifty 
years ; other cases, however, are recorded of anchors having long 
remained amidst coral-reefs without having become coated. The 
anchor of the Beagle, in 1832, after having been down exactly one 
month at Rio de Janeiro, was so thickly coated by two species of 
Tubularia, that large spaces of the iron were entirely concealed ; the 
tufts of this horny zoophyte were between two and three inches in 
length. Spallanzani states (Travels, Eng. Translat. vol. iv. p. 313) 
that in the Mediterranean, the red coral of commerce is usually 
dredged every ten years, during which time it grows to a height of 
one foot. It grows, however, at different, rates in different places. 
It has been erroneously attempted to compute the rate of growth of 
a reef, from the fact mentioned by Captain Beechey of the Chavia 
