THE FLORIDA REEFS. 87 
upon, and their absence is readily accounted for by the con- 
stant disturbance of the shore-line deposits, which reduce little 
by little the larger fragments of shells and corals, or echino- 
derms, to a breccia, or again to oülite or fine sand. This is 
nowhere so well seen as on the shore line of Key West to the 
north of Fort Taylor. (Fig. 53.) There the outer reef is suffi- 
ciently distant to allow waves of considerable size to break upon 
this coast, and then strike to a low line of shore rocks. These 
rocks are completely riddled by larger or smaller cavities made 
by boring mollusks, annelids, sea-urchins, etc., or left by fossils 
or fragments of corals which have fallen out. Thus weakened, 
large masses are easily undermined by the water, which washes 
around them with considerable force. They fall off, become 
then broken into smaller and finer pieces, which are again re- 
ground in their turn, and are finally either re-soldered into finer 
breccia or coarse oülite, or into the finest oülite or sand, accord- 
ing to the composition of the rock. This is then cemented 
again to the shore line, forming a new line, more or less 
regularly stratified, dipping towards the sea, and, when ex- 
posed to the action of the air, soon coated with a thin film of 
hard limestone. This hardens, and forms the ringing crust of 
the rocks found everywhere on the keys. This coating is 
formed with great rapidity. An exposure between two tides is 
sufficient to form such a thin coating, as I have repeatedly had 
occasion to observe in the deposition of finer oólitic sands which 
fill the rock-pockets just within reach of the waves at high tide. 
A process of undermining similar to what has been observed at 
Key West takes place along all the coral-rock shores which 
happen to be exposed to the action of the sea. From the de- 
seription of Rein and others, this undermining action, operat- 
ing on a very much larger scale on :olian deposits of consider- 
able altitudes, must be the principal agent in the formation of 
some of the peculiarly characteristic features of the Bermuda 
Islands. On the east and west shore of Loggerhead, near the 
northern extremity, we ean trace admirably the successive layers 
of the coral limestone which have been deposited and have had 
an opportunity to harden between the tides, forming what ap- 
pear to be stratified beds, with their outerops running as a gen- 
