AGE OF CORAL EEEFS. 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 storm. 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 



