FLORIDA REEFS. 33 



almost entirel}^ of fragments of shells, but the fact that the same shell-con- 

 glomerate occurs at Cape Sable, in the immediate prolongation of the south- 

 ernmost shore bluff, convinces me that one and the same geological 

 formation, identical in lithological character with the reef of Florida, and 

 presenting only slight local modifications, extends all over the penin- 

 sula of Florida, at least as far north as St. Augustine. Leaving this point, 

 for the settlement of which we have not yet sufficient data, let us limit our 

 comparison to the southernmost extremity of the peninsula and the keys. 

 Here, at least, there can be no doubt that the southernmost shore bluff 

 represents another range of keys similar to the main keys lying north of 

 the mud flats, and that the Everglades within those bluffs are in reality 

 another more extensive mud flat, agreeing in every respect with those lying 

 between the main range of keys and the main-land. The only difference is 

 that the Everglades have risen, with time, above the level of the sea. Were 

 the present mud flats partially drained, or were a few additional feet of soil 

 accumulated and consolidated upon them, their depressions would then cor- 

 respond to the swampy ground, and their raised portions to the dry patches 

 on the Everglades, while the Mangrove Islands would represent the hum- 

 mocks. Nor does the agreement end here. About twenty miles from the 

 southernmost shore, within the first prairies, another line of hummocks runs 

 parallel with the first, and with the shore. This ridge, with an instinctive 

 appreciation of its true character, has been called the Long Key. In short, 

 these hummocks and Everglades represent as many ranges of keys divided 

 b}'^ mud flats, showing that the present keys and reefs of Florida are the 

 last of a series of reefs advancing gradually from north to south, in a more 

 or less concentric succession. Endeavoring to reconstruct this process, we 

 should suppose that a long time ago, before the outer reef had grown up 

 from its foundation, the present range of main keys was itself a growing 

 reef, not yet reaching the surface. In the place of the mud flats now filling 

 the space between the keys and the main-land was a channel as deep and 

 unobstructed as that now lying between the main range of keys and the 

 reef. Carrying the scene still farther back to an age for the duration of 

 which we have no measure, the present shore bluffs are then the growing 

 reef, rising to the surface here and there so as to form keys, while the south- 

 ernmost part of the Everglades is changed to an open channel between the 

 Long Key and the shore bluffs. Another backward step, and no reef rises 

 between Cape Sable and Cape Florida, but the ocean beats against the Long 



