30 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



of Cape Florida, Key Biscayne being entirely covered by siliceous sands, 

 just as the beaches of limestone sands cover great tracts of the keys lying 

 to the westward and hide the underlying elevated reef, which crops out, 

 however, on the outer line of keys, as at Sand Key. Shaler speaks 

 of having traced this reef at Old Rhode's and having followed it to the 

 Miami River as an elevated reef. I was quite surprised on examining a 

 bluff about ten feet in height, extending eastward from Cocoanut Point 

 toward the mouth of the Miami River, to find that it consisted of 

 cBolian rocks which have covered the elevated reef in many places. On 

 the low shores these ?eoliau rocks are honeycombed and pitted and 

 might be readily mistaken for decomposed reef rocks ; but they contain 

 no corals. This looks as if the lower southern extremity of Florida, 

 the Everglade tracts, was a huge shallow sink, or a series of more or 

 less connected sinks, into which sand had been blown forming low 

 dunes which have little by little been eroded, and which former observ- 

 ers had mistaken in some localities for reef rock. The material for 

 these dunes coming from the now elevated reef or the beach rock at 

 a time when it was either a fringing or a barrier reef along the former 

 coast line of Florida, all of which, back of the reef, has little by little 

 been eroded by the mechanical and solvent action of the sea, leaving on 

 the mainland only an occasional outcrop of the elevated reef as observed 

 by Professors L. Agassiz and Shaler. The outer line of reef has also 

 been elevated. For I think Tuomey was right in looking upon the out- 

 cropping reef rock of Sand Key as an elevated reef, while Professor 

 Agassiz mistook it. as well as the traces of the elevated reef he saw along 

 some of the keys, for a recent reef consisting of beach rock into which 

 large masses of corals had been thrown by hurricanes. But in this I 

 now think both he and I were mistaken. It was, however, a natural 

 view to take of the formation of that reef for one who was not familiar 

 with the peculiar aspect of the elevated reefs of Cuba. From the Pine 

 Keys and the islands to the west, anil including the Marquesas, there is 

 nothing exposed but beach rock (Plates I.. Y.). stratified at a slight angle 

 seaward on the sea faces of these keys; and even that is only casually 

 exposed, — the greater part of the southern beaches of those keys being 

 covered by coralline and coral sand completely biding the substratum 

 (Plate II.). Behind and upon this Loach rock, BBolian rocks stretch 

 northward and have formed the keys. 



Since my visit the material for the determination of the thickness of 

 the Florida coral reef has been obtained, and we have now accurate data 

 obtained by boring. 



