SECOND ANNUAIy REPORT-SOUTHERN ERORIDA. 
195 
in Whitewater Bay can not be explained by any local peculiarity of 
climate. Rather it is probably the result of the aeration of the thick 
bed of soft gray marl on which they grow by the swing of the tides, 
which here have greater amplitude than anywhere else on the whole 
coast of the peninsula, fully five feet. Northward, toward Cape Ro¬ 
mano, the trees become smaller, and along the inlets back of Caximbas 
they are as bushy as in Whitewater Bay. 
The maximum width of coastal swamp in southern Florida is un¬ 
known, since the boundary between coastal swamp and Everglades is 
a matter of conjecture. After a season of heavy rainfall the channels 
leading from the latter carry fresh water and after a dry season salt 
water. Thus in May, 1908, the writer found salt water in Lostmans 
River within the Everglades, seventeen miles from the mouth of the 
river, while in October of the same year, after the heavy rainfall of the 
summer and early fall the water was fresh several miles nearer the 
Gulf. 
THE KEYS. 
The keys or islands, that fringe the south Florida mainland dififer 
widely in size, shape and surface features. Some are typical barrier 
beaches, long, narrow, low-lying banks of sand with cocoanut palms 
crowning the beach ridg'es, their inner faces hidden in mangrove 
swamps. ' Many are true mangrove islands, shoals formed by the 
efforts of tidal and wind-induced currents where mangroves were able 
to get a foothold and hold material thrown up by the waves. Others 
are sand banks so low lying or exposed as to support only a scanty 
growth of beach grasses and weeds, and still others, notably those in 
the main chain that extends from Virginia Key opposite Miami to Key 
West are of rock or have a rock foundation reaching to or above 
mean sea level and are covered with various scrubby hardwood trees, 
palms, and even pines. 
Within this chain, fringing the mainland or dotted over the Bay 
of Florida are other keys, that can be seen in all stages of growth, 
from banks below sea level to banks just bare at low tide on which 
niangroves have got a foothold and by their entanglement of roots, 
are catching seaweed and drift wood, arresting the movement of sand 
and marl and actively pushing out the shore line. 
Whitewater Bay, which lies behind the Cape Sable foreland and has 
an extreme northwest-southeast length of perhaps twenty miles, is full 
of these mangrove islands, the mangroves on the edges growing out of 
water two feet or so deep. North of Whitewater Bay, the Ten Thou¬ 
sand Islands form an intricate network of channels and of marl banks 
supporting a heavy growth of red and black mangrove. From Big 
Marco Pass to Sanibel Island an almost continuous beach of siliceous 
