of progress of the former, cannot have reached their present condition in less than twenty thousand years.  Their growth must have been successive, since, as we have seen, all Corals need the fresh action of the open sea upon them, and if either of the outer Reefs had begun to grow before the completion of the inner one, it would have effectually checked the growth of the latter.  The absence of an incipient Reef outside of the outer Reef shows these conclusions to be well founded.  The islands capping these three do not exceed in height the level to which the fragments accumulated upon their summits may have been thrown by the heaviest storms.  The highest hills of this part of Florida are not over ten or twelve feet above the level of the sea, and yet the luxuriant vegetation with which they are covered gives them an imposing appearance.

But this is not the end of the story.  Travelling inland from the shore-bluffs, we cross a low, flat expanse of land, the Indian hunting-ground, which brings us to a row of elevations called the Hummocks.  This hunting-ground, or Everglade as it is also called, is an old channel, changed first to mud-flats and then to dry land by the same kind of accumulation that is filling up the present channels, and the row of hummocks is but an old Coral Reef with the Keys or islands of past days upon its summit.  Seven such Reefs and channels of former times have already been traced between the shore-bluffs and Lake Okee-cho-bee, adding some fifty thousand years to our previous estimate.  Indeed, upon the lowest calculation, based upon the facts thus far ascertained as to their growth, we cannot suppose that less than seventy thousand years have elapsed since the Coral Reefs already known to exist in Florida began to grow.  When we remember that this is but a small portion of the peninsula, and that, though we have not yet any accurate information as to the nature of its interior, yet the facts already ascertained in the northern part of this State, formed like its Southern extremity of Coral growth, justify the inference that the whole peninsula is formed of successive concentric Reefs, we must believe that hundreds of thousands of years have elapsed since its formation began.  Leaving aside, however, all that part of its history which is not susceptible 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 us as the lowest possible estimate a period of seventy thousand years for the formation of that part of the peninsula which extends south of Lake Okee-cho-bee to the present outer Reef.