200 
FLORIDA STATE GEOLOGICAL SURVEY. 
ward. This indicated southward drift is probably due to the effective¬ 
ness of the winds from the west and northwest rather than to a pre¬ 
vailing easterly movement of air currents. The great seas of hur¬ 
ricanes and northers are of chief importance in distributing and piling 
up the sand. 
WASTE AND GROWTH OF THE MAINLAND AND KEYS- 
The salient features of the shore line topography of southern Flor¬ 
ida have been summarized, as a detailed relation of the reactions that 
have determined the present outlines of the coast and all the varied 
aspects of the land mass and of the keys lies without the province of 
this paper. But there are features of the growth and waste of the 
land which, as they have been noticed in most descriptions of the topo¬ 
graphy and geology of southern Florida, are here discussed briefly. 
Waste by Solution and Erosion:—The limestones are, as a rule, 
soft and porous. In addition, they are remarkably free from aluminous 
material; hence, they are easily disrupted by tree roots, readily dis¬ 
solved by percolating surface water charged with CO 2 and eroded 
without difficulty by waves and streams. The effects of solution are 
everywhere visible in the outcrops of oolite and coral rock; the pot 
holes, natural wells and springs show how active has been the work 
of underground water. The jagged surface of the Miami oolite 
(described on p. 187), and the bareness of its ridges show how easily 
it dissolves and how free the original sediments were from clay. 
Along the coast, wherever rocks reach the water edge, the waves 
are eating them away. Tidal and wind-made currents carry off part 
of the waste in solution and part in suspension, while the coarser 
detritus is distributed as sand. 
Growth of the Land:—Besides the currents and waves which assort, 
distribute, and pile up the waste of the land, organic ^agencies play an 
important part in extending the shore lines. In fact, such agencies 
are of greater importance in south Florida than in any other part of 
the United States, for here are coral polyps building up rock-like ledges 
strong enough to stand, for a while at least, the hammer of the break¬ 
ers, and mangroves arresting and holding finely-divided material that 
has been swept about by currents. In addition, thick beds of oyster 
shells form banks, hard masses of “worm rock,” the limy tubes se¬ 
creted by a mollusk, protect and extend shore lines, and in addition, 
and perhaps most important of all, the remains of the teeming vegeta¬ 
ble and animal life of the salt water contribute in the aggregate an 
immense amount of material to the upbuilding of the land. 
To the interplay of the agencies of waste and growth above de¬ 
scribed are due those peculiar features of the shore line topography 
