144 Scientific Intelligence. 
even of the coral plantations, these including many and. large 
jarren areas, ‘These unproductive portions of Pecreree con- 
this allowance, the estimate of one-fourth of an a a year would 
become one-twelfth of an i 
Again, shells add pee ee ably to the amount of calcareous 
material, perhaps one-sixth as yee as the corals; but against this 
we may ‘set off the porosity of the coral. 
The rate of growth of the a clivosa, stated on page 
125, would make the rate of increase in the reef very much less 
r. pid. The specimen—grown within fourteen years—weighs 24 
oz. avoirdupois, and has an average diameter of 7 inches. This 
increase would become about 1-80th of an inch per yea 
The specimen of Oculina diffusa, referred to on -_ 125, 
weighs 44 ounces, which is five-sixths more than that of the 
Meeandrina, while the average anaes of the clump is the same. 
The average annual increase would consequently cover a circular 
area of 7 inches diameter 1-18th of an inch deep. And m 
calculation, because we have not the specimen for examination, 
d it is not certain that the Sales stated by him was not 
horizontal diameter. 
These estimates from the Meandrina clivosa and Oculina 
growth as those ip she outer margin of the reef. Again, we have 
made no allowance for the carbonate of lime that is supplied by 
the waters by way of cement, supposing that this must come 
originally, for the most part, from the reef itself. Besides, we 
have aeons supposed all the coral reef-rock to be solid, free from 
open spaces ; and, further, it is not considered that much of it is 
a coral pat soto in which the e fragments 8 their original 
osi 
Pon the other side, we have not allowed for loss of débris from 
the reef grounds by transportation into the deep seas adjoining, 
believing the amount to be very small. 
Whatever the uncertainties, it is evident that a reef increases 
its height or extent with extreme slowness. If the rate of upward 
