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 tlats. 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 different 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 utnaost 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 
Avhich 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 
