THREE CRUISES OF THE ' BLAKE." 
56 
to explain, from a different standpoint, the mode of formation 
of the Florida reefs. Agassiz stated, and his statement was af- 
terward confirmed by Le Conte, that the Florida reefs had a 
distinctive character, and could not be explained by subsidence, 
to which cause Darwin had ascribed the formation of barrier 
reefs in general. In his report! on this subject, Agassiz has 
shown, not only that the southern extremity of Florida is of 
comparatively recent growth, but that the causes by which it has 
for the greater part been built up are still going on, and that 
we have a specimen, as it were, of the past action in the mode 
of growth of the present reef, keys, and mud flats. He shows 
that the whole southern portion of Florida is built of concentric 
barrier reefs, which have been gradually cemented into a con- 
tinuous sheet of land by the accumulation and consolidation of 
mud flats between them,—a process which is now going on 
between the Florida keys and reefs from Cape Florida to the 
Tortugas, and must end in transforming them, in like manner, 
into a continuous tract, to be connected eventually with the 
mainland. 
In Agassiz’s report no attempt is made to explain the sub- 
structure of the peninsula upon which the reef-corals grow. 
Le Conte, however, attributed this substratum to the mass of 
material brought along by the Gulf Stream. He believed that 
the Gulf Stream once ran parallel with the line of the present 
peninsula, and that the substratum was formed by the heaping 
up of these loose materials along that line. All the later in- 
vestigations show, however, that the Gulf Stream never fol- 
lowed this course. Then, as now, it swept across, and not par- 
allel with, the line of the peninsula, and though it undoubtedly 
assisted in the building up of. Florida, it simply brought then, 
as it does to-day, the food, or the greater part of the food, con- 
sumed by the animals living on the Bank of Florida. These 
animals supply, by their growth and decay, the building mate- 
rial for the great Florida Bank. No doubt, the floating ani- 
mals brought by the Gulf Stream add something besides to the 
mass of the bank itself; but they are chiefly consumed by the 
animals living upon it. 
1 Mem. Mus; Comp. Zool. VII. No. I. 1880. 
