186 AGE OF CORAL REEFS. 



about half an inch in ten years. I have col- 

 lected facts from a variety of 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 Mseandrina 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 Mseandrina 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 



