196 
FLORIDA STATF GEOLOGICAL SURVEY. 
sand broken only by narrow inlets, such as Johns Pass, Gordons Pass, 
Big Hickory Pass and Big Carlos Pass, faces the Gulf. These passes 
lead to inner bays dotted with islands of varying size, but possessing 
few features of special interest. 
THE FLORIDA REEF. 
The shores of the main line of keys, extending from opposite Bis- 
cayne Bay to Key West and Boca Grande, in places are rocky, in 
others are bordered by wide flats of marl or calcareous sand. In 
places the surface of the keys is bare rock, in others it is sand or marl. 
Most of the keys have few wide strips of land attaining an elevation 
of as much as six feet above the highest spring tides. 
The longest of the keys, Key Largo, has an extreme length of thirty 
miles, but is nowhere over three miles wide, and the maximum width of 
ground above the level of high spring tides is considerably less. Big 
Pine Key is ten miles long and has an area of high ground nearly two 
miles wide, with a greatest elevation of thirteen feet; while Key West 
is four miles long by one mile wide and the highest ground, which is 
near the center of the city of Key West, has an elevation of thirteen 
feet. The highest point in the whole chain of keys are two small 
knolls, one on Windley’s Island, the other on Plantation Key, just to 
the north. The knoll on Windley’s Island, now partly quarried for 
fills and ballast along the railway line to Knights Key, was eighteen 
feet high. That on Plantation Key was of about the same height. 
A glance at a map of the Florida Keys shows that the islands are 
separated by Bahia Honda Channel into two distinctly differentiated 
divisions. East of, the channel the islands are narrow and lie along 
a sweeping arc curved toward the southeast. Outside this arc is the 
Strait of Florida, inside are the Bay of Florida, Blackwater Sound, 
Card Sound and Biscayne Bay. The western end at Bahia Honda is 
35 miles from East Cape on Cape Sable, the nearest point of the Flor¬ 
ida mainland. The rock ridge of Key Largo is not two miles from the 
edge of the mangrove swamp that fringes the end of the peninsula 
and from there northward the keys are within eight miles of the main¬ 
land. 
West of Bahia Honda the keys form an archipelago roughly tri¬ 
angular in outline. In this bunch of islands, the westward prolonga¬ 
tion of the arc in which lie Bahia Honda and the keys to the east and 
northeast is found in the southern shore line of the keys, but instead 
of lying parallel to this arc the keys themselves have a prevailing north- 
northwest, south-southeast arrangement, perpendicular to the arc. The 
causes of this striking dissimilarity in position are twofold, a difference 
