CORAL REEFS. 31 



process that is going on at its southern extremity now. 

 All that part of Florida which has been examined is 

 found to be formed in this way : first a reef and then 

 i mud-flat, and then a reef and then a mud-flat, one 

 within the other, just as they lie now at the southern 

 end. Seven such reefs and mud-flats have been dis- 

 covered already, and I suppose there are many more 

 in the northern part. Of course, without digging down 

 below the surface and studying the formation of the 

 ground, we could not detect this ; because for centu- 

 ries all traces of those old reefs and mud-flats have 

 been covered with soil and grass, and trees and flowers. 

 We should no more suspect, from its present appear- 

 ance, that Florida had once been the ocean home of 

 the reef-builders, than the people who live centuries 

 after us will suspect that what will then be its southern 

 extremity was, in our time, almost entirely under water. 



You may ask why the little Corals do not settle 

 nearer the shore, and connect their reef immediately 

 with it, instead of beginning at a distance of three 01 

 four miles from the shore, thus leaving a channel to be 

 filled up afterwards by mud-flats. The reason is this. 

 The Corals which form the foundation of the reef de- 

 light in deep water, and could not live in the shallow 

 waters of a sloping shore ; and they like also perfectly 

 clear water, untroubled by the mud and sand washed 

 off from the land by the waves. They naturally seek 

 the conditions most favorable for their growth, and estab- 

 lish themselves at a little distance from the coast, where 

 they find the deeper, purer waters which they need. 



There are other kinds of Corals beside those that I 

 have described here : some that are vegetable, a kind 



