230 
FLORIDA STAFF GEOLOGICAL SURVEY. 
reef. This reef is of the barrier type, separated from the keys by a 
shallow channel caused by the erosion of the elevated reef that shows 
above sea level from Soldier Key to Big Pine Key. The Florida reef 
is terminated at the west by the deep water west of the Tortugas. 
North of Biscayne Bay it dies away in scattered clumps and heacls as 
the waters become too cool for vigorous growth. Fragments of reef¬ 
building corals come ashore on the beach opposite Kobe Sound station, 
and similar coral boulders are said to be washed up by the sea as far 
north as Canaveral Bight. 
While of the barrier type the Florida reef does not rise from the 
sea floor as an almost continuous wall broken by a few narrow open¬ 
ings ; it comprises heads and patches of coral rising irregularly, with 
many intervals where the bottom is covered by coral sand. These heads 
and patches grow in areas separated by breaks, some several miles long, 
where corals are few. The seaward face of these areas lies along an 
arc that in a rough way is concentric to the outer edge of the old reef. 
Along it the corals have grown up from depths of eight to ten fathoms. 
Seaward the bottom falls away and the 100 fathom line is within four 
to ten miles of the line of the outer coral patches. Toward the land in 
water five to twenty-five feet deep, heads and clumps of coral rise to 
the level of low tide several miles inside the arc of the patches. 
At a few places along the reef, as at Sombrero Key, outer patches 
reach to tide level on which the waves have washed up coral sand and 
boulders enough to form small keys, a few rods across, with shifting 
shore lines. Thus the corals build a foundation for dry land, and the 
incipient land growth along the Florida reef led those who first wrote 
of the geology of southern Florida to believe that the keys themselves 
were formed in the same way, without uplift of the coast, and that 
coral reefs had been the principal agency in extending the Florida 
peninsula southward. 
WORM ROCK. 
Aggregations of the limy tubes secreted by a mollusk were seen 
and described by Dali 1 on the west coast. They are particularly notice¬ 
able around the shores of the outer keys between Cape Romano and 
Cape Sable. On the marly sand flats about Rabbit Key between tide 
levels, they form disconnected masses two feet thick, and fifty feet 
wide. 
OYSTER BANKS. 
Banks of solidly-packed oyster shells make reefs at the mouths of 
many rivers, particularly on the west coast. Good examples are found 
at Lostmans River and Caloosahatchee River. 
1 Dali W. H., and Harris, G. D. Correlation Papers; Neocene, U. S. Geol. 
Surv. Bull. 84, p. 153. 
