100 
GEOLOGY: T. IV. VAUGHAN 
tioned, on the piers of Fort Jefferson wharf, and in Fort Jefferson moat. 
The observations in the Bahamas were made on artificially planted and 
naturally attached colonies at the east end of South Bight, Andros Is- 
land. The Florida corals were measured annually; those in the Bahamas 
were measured in 1912 and again in 1914. The average growth rate 
for each species at each station has been computed. The size of the 
colonies of all species of corals seems limited, but some attain large 
dimensions, 2 to 3 meters or even more in diameter, and nearly as much 
in height, while other species are adult when a diameter of 35 to 50 mm. 
has been reached. Favia fragum and Maeandra areolata are instances of 
species which grow relatively rapidly for the first 2 to 4 years, after which 
they grow more slowly. Orhicella annularis and Maeandra strigosa 
are not so limited in size. Branching corals grow more rapidly than 
massive species; while of the former, the growth rate of species with per- 
forate, loose-textured skeletons is more rapid than that of species with 
dense skeletons. In general the more massive and the denser the coral- 
lum, the slower the growth; while the more ramose and the more porous 
the skeleton, the more rapid the growth. 
There is no average growth rate for corals generally speaking, as growth 
rate varies from species to species, and varies for the same species ac- 
cording to local environmental conditions. Here it may be said a 
colony of species of reef coral in a lagoon, if protected from sediment, 
may grow more rapidly than a colony of the same species does on the 
reef. The limitation of reef corals so largely to the outer edges of plat- 
forms is determined primarily by purity of water, i.e., freedom from silt, 
and by the more uniform temperature. 
In order to estimate the rate at which a reef will grow, the upward 
growth rate of the true reef-forming species must be taken. The up- 
ward growth rate of Orhicella annularis, the principal builder of the 
Pleistocene and living reefs in Florida and the West Indies, is from 5 to 
7 mm. per year, according to station. At 6 mm. per year, it would 
form a reef 150 feet thick in 7620 years; at 7 mm. per year it would build 
the same thickness of rock in 6531 years. Acropora palmata, which 
grows more rapidly, might build a similar thickness in 1800 years. 
The growth of corals in the Pacific appears to be more rapid and ac- 
cording to Stanley Gardiner they might build a reef 150 feet thick in 
1000 years. The investigation of the growth rate of corals shows that 
any known living coral-reef might have formed since the disappearance 
of the last continental ice sheets. 
fThis summary is published by permission of the President of the Carnegie Institution 
of Washington and of the Director of the U. S. Geological Survey.) 
