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AGASSIZ: THE FLORIDA ELEVATED REEF. 43 
considerable velocity, and in our dredgings we brought up only a few 
specimens of coralline alge, the current sweeping everything before it. 
Soldier Key is the most easterly of the patches of elevated reef. 
To the north and south of it the reef has been partly eroded and partly 
covered over by the sand bores which flank the deep channels that have 
been cut through the elevated reef to give passage to the mass of water 
which pours out from Key Biscayne Day (Plate ХІП.). This is 
saturated with vegetable matter, and holds in suspension and in so- 
lution a great amount of lime, the former of which is deposited in the 
sand bores, and the other carried to sea, or perhaps precipitated under 
favorable conditions. 
The shore of the sea face of Key Biscayne consists of siliceous sand, 
though a bank of coquina must be forming on an outside bar off the 
island, judging from the many fragments of it scattered on the beach. 
The siliceous sands form patches of solidified rock round the roots of 
trees and shrubs washed by the sea; some of these patches of harder 
material are of considerable extent, and appear at first sight like a bank 
of tubular sponges thrown up on the beach, The large amount of lime 
carbonate held in solution in the sea water undoubtedly forms with the 
siliceous sands the hard material mentioned above. Steaming parallel 
with the shore of the mainland we could follow the low rounded molian 
hills flanking the sea face of the mainland from the bluff to the south 
of the mouth of Miami River to west of Cocoanut Grove, The hills are 
separated by narrow patches of mangrove swamps, similar to those we 
examined south of the mouth of the Miami River, where the eolian rocks 
barely reached the surface. It will be an interesting question to deter- 
mine how far the “hummocks” are eolian ҺИ, "and how far they are 
patches of the elevated reef, as well as to determine where the molian 
hills crop out along the coast line of the mainland from Key Biscayne 
to Cape Sable, and how far inland they extend. We still have to 
determine how far the Everglades are a part of a great system of sinks 
formed, as were those of the Bahamas, by the disintegration, erosion, and 
solution of the molian drift rock, and how far inland we can trace patches 
of a single or patches of a series of elevated reefs. What has been 
observed thus far along the line of the Keys, and along the southern 
edge of the mainland of Florida, by L. Agassiz, Shaler, and. myself, 
seems to indicate the former existence of a wide belt of edging reefs and 
reef patches off the line of the mainland when its southern limit was 
1 See the Notes of L. S, Griswold, and the view I take of his observations, 
page 54. 
VOL. XXVIII. — NO. 2, 2 
