58 FLOKIDA EEEFS. 
began. Leaving aside, however, all that part of its history which is not sus- 
ceptible of positive demonstration in the present state of our knowledge, I 
will limit my results to the evidence of facts already within our possession ; 
and these give ns as the lowest possible estimate a period of seventy thou- 
sand years for the formation of that part of the peninsula which extends 
south of Lake Okee-cho-bee to the present outer reef. 
So much for the duration of the reefs themselves. What, now, do they 
tell us of the permanence of the species by which they were formed ? In 
these seventy thousand years has there been any change in the corals livino- 
in the Gulf of Mexico ? I answer most emphatically, Av. Astrasans, Porites, 
Moeandrinas, and Madrepores wei'e represented by exactly the same species 
seventy thousand years ago as they are now. Were we to classify the 
Florida corals from the reefs of the interior, the result would correspond 
exactly to a classification founded upon the living corals of the outer reef 
to-day. There would be among the Astrjeans the different species of 
Astri»a (PI. IV.) proper, forming the close, round heads, — the Mussa, grow- 
ing in smaller stocks, where the mouths coalesce and run into each other as 
in the Brain-Corals, but in which the depressions formed by the mouths are 
deeper, — and the Caryophyllians (Cladocora PI. III., Figs. 1-7), in which 
the single individuals stand out more distinctly from the stock: amono- 
Porites, the P. Astrajoides (PI. XVL, Figs. 1-12), with pits resembling those 
of the Astra3ans in form, though smaller in size, and growing also in solid 
heads, though these masses are covered with club-shaped protrusions, instead 
of presenting a smooth, even surfiice like the Astrasans, — and the P. Cla- 
varia (PL XII., Figs. 4, 5, and 6), in which the stocks are divided in short, 
stumpy branches, with club-shaped ends, instead of growing in close, com- 
pact heads; among the Mi^andrinas we should have the round heads we 
know as Brain-Corals (PL IX.), with their wavy lines over the surfiice, and 
the Manicina (Pis. V., VI.), differing again from the preceding by certain 
details of structure ; among the Madrepores we should have the Madrepora 
prolifera (PL XIX.), with its small, short branches," broken up by very fre- 
quent ramifications, the M. cervicornis (PI. XVIII.), with longer and stouter 
branches and less frequent ramifications, and the cup-like M. palmata (PL 
XVII.), resembling an open sponge in form. Every species, in short, that 
lives upon the present reef is found in the more ancient ones. They all 
belong to our own geological period, and we cannot, upon the evidence 
before us, estimate its duration at less than seventy thousand years, durino- 
