i8o CORALS AND CORAL LSLANDS. 



The stratification is somewhat irregular, the beds slanting 

 toward the sea at an angle of about seven degrees. Upon this 

 foundation immense masses of Strombus, dead shells, and 

 corals have been thrown in banks, evidently the beginning of 

 deposits similar to those already consolidated below ; but there 

 is this difference in their formation, namely, that while the 

 foundation rock is slightly inclined, and never rises above the 

 level of high water, the accumulation 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 accumu- 

 lation 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 {Batatas littoralis)^ various grasses 

 and shrubs are the most conspicuous. These dunes rise to 

 about twenty feet ; on tlieir lee side and almost to their summits 

 grow 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 is a pool of intensely salt 

 water, the tint of which is pinkish or flesh-coloured, owing to 

 the accumulation of a small alga. When agitated by the wind, 

 this pool is edged 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 odour. The 

 foundation rock of this Key is exactly like what Gressly de- 

 scribed as the 'fades corallien ' of the Jurassic formation ; while 

 the deposit in deep water, consisting chiefly of muddy lime 

 particles, answers to his 'fades vaseux' 



" Double-Headed Shot Key is a long, crescent-shaped ridge 

 of rounded knolls, not unlike ' roches moutoimees' at intervals 

 interrupted by breaks, so that the whole looks like a dismanded 



