7 6 FLORIDA GEOLOGICAL SURVEY—FOURTH ANNUAL REPORT. 
The marine marshes being within the range of the tides, can be 
reclaimed only by diking, although if reclaimed they would un¬ 
doubtedly prove very fertile. The fresh water marshes afford condi¬ 
tions favorable to the accumulation of vegetable matter and are 
frequently underlaid by deposits of muck. 
The muck and fresh water marsh lands of Florida are extensive, 
aggregating not less than 5,000 square miles. The Everglades of 
southern Florida include the most extensive single area of muck 
lands, although many smaller areas occur throughout the State. 
THE EVERGLADES. 
The Everglades occupy the greater part of southern Florida. 
From Lake Okeechobee on the north they extend south to the Gulf 
of Mexico, a distance of 90 to 100 miles. Their maximum width is 
possibly 50 miles, although their average width is somewhat less. 
The boundaries, especially on the south and west, are more or less 
indefinite and irregular which makes it difficult to give a close esti¬ 
mate of their area. On the east they extend to within five to ten 
miles of the coast, their boundary being formed by a ridge of oolitic 
limestone rock, the Miami Limestone. Numerous streams originating 
in the ’Glades cut across this rim. Among these are Hillsboro River, 
New River, Miami River, Cypress Creek, and Snake River. To the 
south the boundary is less definite, as the ’Glades change character 
more or less approaching the Gulf, although in places the saw grass 
marsh reaches to the mangrove swamps bordering the coast. On the 
west side, the Everglades give place to cypress, prairie and pine 
lands. The total area of the Everglades is between 4,000 and 5,000 
square miles. 
The elevation of Lake Okeechobee at the head of the Everglades, 
has been determined by careful surveys. The level of the lake at the 
head of Okeechobee Canal was determind as 20.4 feet above mean 
low water in the Gulf of Mexico in 1901. Other levels made at va¬ 
rious times indicate that the lake varies in level between high and 
low water stages from about 10 to 22^ or 23 feet. The Everglades 
which slope away from the lake toward the Atlantic and Gulf coasts 
receive the overflow from the lake. 
The southern part of Florida was elevated above sea level during 
or at the close of the Pleistocene period. The Miami Limestone 
which underlies a part of the ’Glades and forms its east rim is, as 
previously stated, of Pleistocene age. On the west side of the ’Glades 
Pleistocene shell deposits are found at the head of the Caloosa- 
