112 Papers front the Marine Biological Laboratory at Tortugas. 



of the latter. Its lower boundary is formed by spurs from the mainland 

 and Key Largo. This sound is quadrangular in outline; length 4 miles, 

 width 3.5 miles, maximum depth 9 feet. 



Hoodoo Sound is a small body of water lying within the western 

 part of the spur of Key Largo, which forms the southern boundary of 

 Blackwater Sound. It has a length of 1.5 miles, width 0.5 mile, depth 

 8.5 feet. 



Florida Bay is of cornucopia shape, with its narrower end at the 

 western outlets of Blackwater and Hoodoo sounds. The width of the 

 upper end is about 10 miles; it opens toward the west and is 27 miles 

 wide south of Cape Sable. The water also deepens toward the west 

 from 4 to 7 feet, at its upper end, to 10 to 12 feet between Cape Sable 

 and Key Vaca; farther westward it deepens to 12 to 14 feet, and then 

 gradually slopes to the lo-fathom line in the Gulf. 



Keys, Mud Flats, and Shoals in the Bays and Sounds. — Here it need 

 only be mentioned that behind the main keys and betweeen them and 

 the mainland are keys mostly overgrown with mangroves, mud flats 

 exposed at low tide, and shoals built almost to water-level. The axes 

 of these keys and banks trend from north to south, at right angles to 

 the main keys, which are elongated from northeast to southwest. Their 

 origin will be especially discussed in succeeding pages. 



To summarize the features occurring between the 10-fathom curve 

 and the shore of the mainland, there are: 



(i) The reefs lying just inside the lo-fathom curve. 



(2) The Hawk Channel, separating the reefs from the main line of 



keys, varying in width from 3 to 7 miles and having a maximum 

 depth of 5 or 6 fathoms. 



(3) The main keys. 



(4) The bays and sounds separating the keys from the mainland. 



RELIEF OF THE MAINLAND. 



In the following remarks the physiography of the mainland will 

 not be treated in detail, the purpose being to consider the land surface 

 as only a subaerial portion of the more extensive Floridian Plateau. 

 Matson and Clapp have compiled a topographic map of the State, with 

 So-foot contour intervals. This map, although it does not claim to be 

 without minor inaccuracies, gives the best available information on the 

 relief of the land surfaces. (Plate i, the subaerial topography.) 



Florida is a land of low relief, perhaps two-thirds of it lying below 

 the 50-foot contour. This hne extends far up St. Mary's River on the 

 northern boundary of the State, whence, proceeding southward, it passes 

 about 9 miles west of Jacksonville and through Palatka on the west side 

 of St. John's River. On the east side of the latter river, from just below 

 Palatka to the latitude of Lake Monroe, it circumscribes a ridge. It 

 continues down the west side of St. John's River, extending up its tribu- 

 taries and passes well to the north of Lake Okeechobee, at least 15 or 20 

 miles. On the western side of the Peninsula it lies above the level of 

 Arcadia on Peace River; it passes around the head of Tampa Bay, thence 



