186 AGE OF CORAL REEFS. 
about half an inch in ten years. I have col- 
lected facts from a variety 6f sources and local- 
ities that confirm this testimony. A brick placed 
under water,in the year 1850, by Captain Wood- 
bury of Tortugas, with the view of determining 
the rate of growth of Corals, when taken up 
in 1858 had a crust of Meandrina upon it a little 
more than half an inch in thickness. Mr. Allen 
also sent me from Key West a number of frag- 
ments of Meandrina from the breakwater at 
Fort Taylor ; they had been growing from twelve 
to fifteen years, and have an average thickness 
of about an inch. «The specimens vary in this 
respect, —some of them being a little more than 
an inch in thickness, others not more than half 
an inch. Fragments of Oculina gathered at the 
same place and of the same age are from one 
to three inches in height and width; but these 
belong to the lighter, more branching kinds of 
corals, which, as we have seen, cannot, from their 
brittle character, be supposed to add their whole 
height to the solid mass of the Coral wall. Mille- 
pore gives a similar result. 
Estimating the growth of the Coral Reef ac- 
cording to these and other data of the same 
character, it should be about half a foot in a 
century ; and a careful comparison which I have 
made of the condition of the Reef as recorded 
in an English survey made about a century ago 
