FLORIDA REEFS. 35 
of paramount importance, were it only with reference to the position of 
lighthouses. But there is another subject connected with this investiga- 
tion which is not less momentous. It is well known that, in the Pacific, 
coral reefs have been raised above the levels at which they were formed, by 
the agency of the living animals, and also that in other localities, sometimes 
in close connection Avith those just mentioned, the ground is subsiding. 
These changes have been so often observed, whenever coral reefs occur, that 
the idea of subsidence and upheaval is naturally connected with the features 
of coral reefs, and the question at once arises, whether the reefs on our 
shores are thus undergoing variations of level, independently of their 
natural growth. ^Ye have seen how extensive are the changes produced 
merely by the normal growth of the corals, and the facts accompanying 
their increase. It now remains for us to ascertain Avhether this growth has 
taken place, or does at present take place, upon ground which has 
chang-ed or is now chano-ino; its relative level in reference to the sea. 
The facts already described afford a sufficient answer to the question. 
We are satisfied that as far as coral formations have been observed upon the 
main-land of Florida, and within the present extent of the coral reefs, no 
change of the relative level has taken place either by subsidence or up- 
heaval of the coral ground, and that all the modifications which the reef has 
presented at successive periods have been the natural consequence of the 
growth of reef-building corals, with the subsequent accumulation of their 
products in the manner described above. 
I am sorry to difier from my friend, Mr. Tuomy, who, in an interesting 
account of an excursion to Florida, considers the upright coral heads stand- 
ing above the water level as evidence of the upheaval of the reef I have 
already shown that, although at the first glance the position of these heads 
suggests that they have grown where they are found, they are, in fact, 
detached boulders, acciunulated where they now lie. Setting this aside, the 
whole coral field of Florida furnishes connected evidence that neither up- 
heaval nor subsidence of the ground on which the coral formations rest has 
taken place. The maximum height of all these formations including 
the bluffs on the main-land, is the same, — between twelve and thirteen 
feet above high-water mark. If we ascribe their present level to a series of 
upheavals rather than to the natural accumulation on the spot, we must 
suppose each successive disturbance to have raised the more recent reef and 
range of keys to exactly the same height as the earlier ones, without in the 
