SECOND ANNUAL REPORT-SOUTHERN FLORIDA. 
201 
of southern Florida which have been noticed on a previous page. The 
special significance of those features in this connection is that the 
agencies which wear away the land and those that extend it have not, 
in most accounts of the geology of the region under discussion, been 
sharply discriminated, or one group has been given undue importance 
in comparison with the other. 
As an instance may be cited the southern growth of the” mainland 
and the character of the mangrove islands along the northern part of 
the Bay of Florida and in Blackwater and Card Sounds. The bed rock 
floor of limestone that outcrops in the Biscayne pineland, on Long Key, 
and adjoining keys in the Everglades, slopes gently to the south. On 
it the marls, sandy beaches of Cape Sable and below the prairie back 
of Flamingo, those of the mangrove swamp to the east and of the man¬ 
grove islands in the bay, now rest. Hence, these islands and the pro¬ 
jecting tongues of swamp along Blackwater Sound can hardly be 
erosion remnants of a former continuous land surface. Rather do they 
represent the work of agencies, which, if unchecked by a depression of 
the coast, will ultimately join the mainland to the keys. 
EVIDENCES OF RECENT CHANGES OF LEVEL. 
While the accumulated evidence shows that the Pleistocence and 
Recent history of Florida has been marked by no great disturbances, 
that the elevations or depressions of the land, though affecting great 
areas have been of relatively small amount, and while there is no 
reason to suppose that the region will be violently disturbed in the im¬ 
mediate future, yet as the question of relative permanency of height of 
land is of importance because slight changes with respect to sea level 
will have a pronounced effect on the habitability of the coasts, the 
evidence available is briefly summarized. 
That the coast line has been elevated the old coral reef of the 
Florida keys is abundant proof. That it has been slightly depressed 
since the maximum elevation is indicated by solution cavities in the 
limestones extending considerably below water level and by the rela¬ 
tion of the dunes to present shore lines. 
As to more recent changes and the present movement we have the 
evidence of swamps, of shore lines and of human records. 
If the swamps are being depressed there should be tree trunks of 
the older forests buried beneath the sediments that have accumulated 
since the trees fell. The writer noted a thick stump in gray marl at 
one of the numerous entrances to Shark River, near the plant of the 
Minetto Lumber Company. It was about three feet below the present 
surface of an islet, which is covered by water at high tide. The evi¬ 
dence was not conclusive, as the log might have drifted to its resting 
