2896.1 417 [Gushing. 



Plate XXVI. 



The view presented on Plate XXVI illustrates the appearance 

 of certain shoals and islets to the eastward of Key Marco, in the 

 northwesterly edge of the Ten Thousand Islands. It admirably exhib- 

 its the form of an original oyster-bar or coral-reef, as defined by 

 the lines of foam caused by the rapidly retreating tide. It will be 

 observed that these lines enclose a central space of deep water (between 

 the two black masses of reef-crags already exposed), and that these 

 foam lines extend off laterally, forming an irregular, atoll-like, or 

 semicircular enclosure, that greatly resembles the outline or plan of a 

 true, built up or artificial key, or shell settlement. 



For this and other reasons — discussed at length on pp. 335 to 837, 

 inclusive, and incidentally elsewhere in the text — it is supposed that the 

 earliest key-builders made the beginnings of their great shell structures 

 or islands (such as are mapped on Plates XXVIII and XXX) upon reefs 

 and shoals like these. 



The appearance, seen from a distance, of these shell islets or keys, when 

 overgrown and surrounded by mangroves, as nearly all of them are, 

 is quite well shown toward the left, and also at the extreme right, of 

 the picture. 



