BETWEEN FLORIDA AND CUBA. Ds 
evidently the beginning of deposits similar to those already 
consolidated below; but there is this difference in their for- 
mation, namely, that while the foundation rock is slightly 
inclined, and never rises above the level of high water, the ac- 
cumulation of loose materials above water-level forms steeper 
banks, varying from fifteen to twenty and thirty degrees. In 
some localities broken shells prevail; in others, coarse and 
fine sand; and the ridges thus formed, evidently by the action 
of high waves, rise to about twelve and fifteen feet. This is 
evidently the foundation for the accumulation of finer sand 
driven by the wind over these ridges, and forming high sand- 
dunes, held together by a variety of plants, among which a 
trailing vine (Latatas littoralis), various grasses, and shrubs 
are the most conspicuous. These dunes rise to about twenty 
feet ; on their lee side and almost to their summits grows a 
little palmetto. The sand of the dunes is still loose, but here 
and there shows a tendency to incrustation at the surface. 
The slope of these dunes is rather steep, sometimes over 
thirty degrees, and steeper to the seaward than on the land- 
ward side. 
‘In the interior of Salt Key there 1s a pool of intensely 
salt water, the tint of which is pinkish or flesh-colored, owing 
to the accumulation of a small alga. When agitated by the 
wind, this pool is hedged all around by foam of the purest 
white, arising from the frothing of the viscous water. Along 
the edge the accumulation of this microscopic plant forms 
large cakes, not unlike decaying meat, and of a very offensive 
odor. The foundation rock of this Key is exactly like what 
Gressly described as the ‘facies corallien’ of the Jurassic 
formation; while the deposit in deep water, consisting chiefly 
of muddy lime particles, answers to his ‘facies vaseux.’ 
“ Double-Headed Shot Key is a long, crescent-shaped 
