5 
AGASSIZ: THE FLORIDA ELEVATED REEF. 3 
by a coralline bottom, on which are found scattered specimens of Mæan- 
drina, coarse fragments of Astreans, Behini, and corallines such as 
Udotea and Halimeda mainly. The bottom is of a similar character 
halfway between Washerwoman Buoy and Boca Chica. In the middle 
of the main channel, all along the reef, the same coralline sand is usually 
found thickly packed with Udotea and Halimeda. 
At Sand Key we found the reef rock elevated fully two feot above 
high-water mark. The parts of the former elevated reef form a series 
of pinnacles, on the sea face of which corals are now growing. The 
central part of the key is covered by a mass of fragments of corals 
of all sizes, finely ground with sand, and thrown up to a height of 
about eight feet. Much of the elevated reef is often uncovered by 
hurricanes, as was the case during the hurricane of September, 1894, 
when the sea washed over the whole island. The elevated reef of which 
Sand Key forms a part was evidently not raised to as great a height as 
the ancient reef farther north. At Sand Key it is not difficult to dis- 
tinguish between the elevated reef and the living reef, the line of 
demarcation is quite sharp. 
At Sombrero Key we could not separate the elevated reef from its 
coating of recent corals, especially since a good deal of coral had evi- 
dently been killed by exposure to the air. But off Sombrero Light we 
found old elevated reef rock honeycombed and pitted, and surmounted 
by growing heads of coral, just as we had observed them at the Hen 
and Chickens. 
An examination of the Chart (Plate XVI.) shows that the shores of 
the islands which stand opposite great gaps in the reef are all covered 
with coral sand, as, for instance, in the great stretch between American 
Shoal and Alligator Reef, where the shores are exposed to the sweep 
of the sea, which throws up at times great masses of coral and coralline 
sand, covering the elevated reef. This undoubtedly extended in a more 
or less continuous stretch all the way along the former shore line of the 
southern face of Florida. It has, however, at some points, been little by 
little covered by the sand thrown up from the stretches exposed to the 
sea, and at others the wearing action of the sea has broken through 
the roof and formed the shallow passages which now separate adjoining 
islands. 
East of Alligator Reef the main line of keys is far more sheltered, a 
nearly continuous reef stretching from that point as far as Fowey 
Rocks, there being only an occasional gap in the broad reef. This 
streteh of the reef is in striking contrast to the narrow and insignificant 
