SECOND ANNUAL REPORT-SOUTHERN FLORIDA. 
215 
In 1883 A. Agassiz published a paper on the keys, in which he at¬ 
tributed their western growth to a return eddy of the Gulf Stream, 
previously postulated by Hunt, and said 1 (pages 108-109) : “The line 
of keys seems to be formed by the waste of the exterior present reef 
rather than by the remains of an older reef.” He recognized that the 
Tortugas were younger than the keys to the east, saying that the de¬ 
posits composing them “have not as yet been transformed into the 
normal coral rock.” 
On a subsequent visit to the keys, Agassiz saw the evidences of 
elevation and confirmed the conclusions of Tuomey. 2 He elaborated 
his views of the growth of the keys in the most comprehensive ac¬ 
count of their geology and topography that has yet appeared. 3 
The recent construction work of the Florida East Coast Railway 
has shown the character of the rock from where the railroad bends 
southwest on Key Largo to the west end of Knights Key. Borrow pits 
expose the limestone not only where it was lightly covered by leaf 
mould but where buried under several feet of marl and sand, and have 
determined its character where it lies, as in channels between the keys, 
ten feet or more below sea level. Hence, the opportunity for observing 
the various phases of the rock and for determining its origin is in¬ 
comparably better than when A. Agassiz visited the keys in 1894. 
On Key Largo, cuts and borrow pits expose the limestone at fre¬ 
quent intervals from the south shore of Lake Surprise to the west end 
of the island at Tavernier Creek, a distance of fifteen miles. As this is 
the longest series of exposures on any of the keys, the reef rock is 
here designated the Key Largo limestone. 
Stratigraphic Position:—As the Key Largo limestone represents 
the only known fossil coral reef in southern Florida it forms a litho¬ 
logic unit and is sharply differentiated from any of the other lime¬ 
stones of the mainland and keys. Having been built up from the bot¬ 
tom from a depth perhaps of over 100 feet during a considerable in¬ 
terval of time, it may in part be contemporaneous with the other lime¬ 
stones, and in part may be older, as these limestones are believed to 
represent shallow water deposits, some of which accumulated behind 
the reef while the latter was growing and finally extended over it. In 
places the Key West oolite apparently rests on the Key Largo lime¬ 
stone ; the relations to the Miami oolite and the Lostmans River lime¬ 
stone are less certain. 
1 Agassiz, Alexander. The Tortugas and Florida Reefs; Am. Acad. Mem. 
II, 1883, pp. 107-134. 
2 Agassiz, Alexander. Note on the Florida Reef; Amer. Jour. Sci. (3) xlix, 
1895, pp. 154-155. 
3 Agassiz, Alexander. The Elevated Reef of Florida; Mus. Com. Zool. Bull. 
XXVIII, No. 2, 1896, pp. 29-62. 
