34 FLORIDA REEFS. 
Key, then a growing reef. Here we will stop, since our knowledge of the 
interior is not sufficiently exact to justify us in pushing our retrograde his- 
tory farther. Let us reverse the process now, and, starting from Long Key 
as the then southernmost point of Florida, build seaward. Twelve or 
twenty miles from the shore the sea has a depth of some twelve to twenty 
fathoms, and there a reef begins to grow. Gradually it rises, till here and 
there it reaches the sea level in patches. On such patches broken frag- 
ments of coral, sand, and mud accumulate, and they are gradually fashioned 
into keys. Between this growing reef and Long Key there flows at first 
a channel ; but by the accumulatiou of coral sand, mud, and debris of all 
sorts, from the reef or from the main-land, this channel is gradually trans- 
formed into a tract of mud flats. These flats are gradually raised to the sur- 
face of the water, and they, as well as the shore bluffs, become dry land. 
Perhaps before this process comes to an end another reef begins to rise, the 
conditions for its formation being pushed a little farther south by the shore 
bluffs themselves, since the corals prosper only on a certain slope and at 
a certain distance from the land. The foundation for the main range of 
keys is now laid ; but the tract now occupied by the mud flats is still open 
sea, the powerful action of which we may trace to this day in the excava- 
tions and erosions of the shore bluffs. At last this new reef reaches the sur- 
face, here and there gradually forming the present main range of keys, 
while the open channel is transformed, by accumulation, into the present 
mud flats. The main range of keys, like the shore bluffs, determines the 
position for the next coral wall, and the present outer reef begins to rise, 
though nearer to the main range of keys then they had been to the sliore 
bluff, because the sea bottom is steeper. As this last reef rises, it modifies, in 
its turn, the course of the surrounding waters, the channel between it and 
the keys begins to fill, the shoals encircling the islands increase, and we 
arrive at last at the present condition of things. We have thus followed the 
extension of the peninsula of Florida, through the successive annexation of 
a series of coral reefs, the most recent of which is still in the stasre of active 
and rapid growth. 
But it may be asked. What is the practical use of such detailed descrip- 
tions of the coral reefs for the coast survey ? We need only allude to the 
universal impression of the dangers arising to navigation from the growth 
of such reefs to satisfy the most sceptical that a minute knowledge of the 
extent and mode of formation of those belonging to our own shores must be 
