FLORIDA REEFS. 3 



keys are literally studded with these Mangrove Islands. Sometimes they 

 are distributed without apparent regularity ; sometimes, as to the north 

 of Key Largo, they form a continuous range between the main-land and 

 the keys. They are also very numerous along the main keys, or at 

 least along that side of them which is turned towards the most extensive 

 mud flats. Sometimes these Mangrove Islands form little archipelagoes 

 of innumerable small islets, so intimately interwoven, and separated by such 

 narrow and shallow channels, as to be almost impenetrable. Such archipela- 

 goes occur chiefly to the north of Bahia Honda and the Pine Islands, as well 

 as to the northwest of Key West. The luxuriant vegetation which rises 

 from these low islands, consisting chiefly of mangroves, gives them a very 

 peculiar appearance. We shall have occasion to return to this subject 

 when we attempt to explain the formation of the diJBferent islands connected 

 with the Florida Reef and the main-land. The whole tract between Cape 

 Sable and the keys, east of Bahia Honda, as far as Cape Florida, or at least 

 as far as Soldier Key, is so shoal that it will forever remain inaccessible, 

 except to very small vessels. 



The keys consist of an extensive range of low islands, rising but a few 

 feet, perhaps from six to eight or ten, or at the utmost to twelve or thirteen 

 feet, above the level of the sea. They begin to the north of Cape Florida, 

 where they converge towards the main-land, extending in the form of a flat 

 crescent in a southwesterly direction, gradually receding from the main-land 

 until, opposite Cape Sable, they have so far retreated as to be separated 

 from it by a shallow sheet of water forty miles wide. Farther to the west 

 they project in a more westerly course, with occasional interruptions, as far 

 as the Tortugas, which form the most western group. They consist either 

 of accumulated dead corals, of coral rocks, or of coral sand, cemented 

 together with more or less compactness. Their form varies, but is usually 

 elongated and narrow, their greatest longitudinal extent following the direc- 

 tion of the main range, except in the group of the Pine Islands, where their 

 course is almost at right angles with the main range, — a circumstance 

 which we shall attempt hereafter to explain. 



Most of these islands are small, the largest of them, such as Key West 

 and Key Largo, not exceeding ten or fifteen miles in length ; others only 

 two or three, and many scarcely a mile. Their width varies from a quarter 

 to a third or half a mile, the largest barely measuring a mile across ; but 

 whatever the difference in their size, they all agree in one respect, — that 



