AGE OF CORAL REEFS. 181 
Such caps of soil on the summit of a Coral 
Reef are of course very insecure, till they are 
consolidated by a long period of accumulation, 
and they may even be swept completely away by 
a violent stoim. It is not many years since the 
light-house, built on Sand Key for the greater 
security of navigation along the Reef, was swept 
away, with the whole island on which it stood. 
Thanks to the admirably conducted investigations 
of the Coast-Survey, this part of our seaboard, 
formerly so dangerous on account of the Coral 
Reefs, is now better understood, and every pre- 
caution has been taken to insure the safety of 
vessels sailing along the coast of Florida. 
I cannot deny myself the pleasure of paying a 
tribute here to the high scientific character of the 
distinguished superintendent of this survey, who 
has known so well how to combine the most im- 
portant scientific aims with the most valuable 
practical results in his direction of it. If some 
have hitherto doubted the practical value of such 
researches, —and unhappily there are always 
those who estimate intellectual efforts only by 
their material results, — one would think that 
these doubts must be satisfied, now that the 
Coast-Survey is seen to be the right arm of our 
navy. Most of the leaders in our late naval ex- 
peditions have been men trained in its service, 
and familiar with all the harbors, with every 
