BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY, 
Notes on the Geology of Southern Florida. By Lzow S. GRISWOLD. 
(Plates XVII. to XXVI.) 
The Ocean Border, — The southeastern extremity of Florida is pro- 
tected on the side toward the ocean by an almost continuous line of 
narrow islands, — the Florida Keys. Between these islands and the main- 
land there is a continuous shallow water body, constricted for short 
intervals to a width of a hundred yards or less, but generally some miles 
in width, even to twenty-five miles. Bars and flats (Plate XXI. Fig. 1), 
with or without aerial vegetation, divide this large water area into a 
multitude of small sounds. In many places, at depths of five to twelve 
feet, the floor of these sounds is rock ; the floor is not smooth, yet affords 
no anchorage. An idea of the sea floor may be had from Plate XVIII. 
of the shore at Cocoanut Grove at half tide. (See also Plate П.) 
The Foundation of the Mainland. — On approaching the mainland on 
Key Biscayne Bay the rock floor comes near the surface, so that speci- 
mens may be obtained. The rock is no longer elevated reef, but a fine 
grained oólitic limestone, containing occasional shells and supporting à 
growth of southern pine. Shore line bluffs and vertical seotions ob- 
tained inland show stratification clearly, and for the most part cross- 
bedding. (Plate XIX.) Тһе deepest section obtained, sixteen feet in 
a well at Cocoanut Grove, showed numerous fragments of coral at the 
bottom. This would tend to indicate that the odlite covers a reef. Тһе 
bottom of the well is about at sea level, and variations in the height of 
the sea water affect the depth of water in the well. This fact is general 
at Cocoanut Grove. 
If we can assume a broad reef as underlying the oólite, then there is 
a long narrow uplift along the line of great keys, or there is a line of 
dislocation just on the west side of these keys, the upthrow being to the 
east. Analogy with the phenomena of the mainland would favor the 
idea of folding. 
The Pine Belt. — The rise of the oólite from the sea is gradual, vary- 
ing up to about four feet in a hundred. Bluffs even ten or twelve feet 
high occur where conditions are favorable for shore cutting, and there 
are old bluff lines now protected by marsh. The bluff condition pre- 
vails for some miles south of the Miami River; north and south of this 
1 This bluff is a most distinctly marked molian rock exposure, with character- 
istic knife edge stratification. — A. AGASSIZ. 
