AGASSIZ: THE FLORIDA ELEVATED REEF. 43 



considerable velocity, and in onr dredgings we brought up only a few 

 specimens of coralline algae, 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 hank 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 Bay (Plate XIII.) . 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 seolian 

 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 eeolian rocks 

 barely reached the surface. It will be an interesting question to deter- 

 mine how far the "hummocks" are seolian hills, 1 and how far they are 

 patches of the elevated reef, as well as to determine where the a?olian 

 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 teolian 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 



