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 
eolian rocks which have covered the elevated reef in many places. On 
the low shores these æolian 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 outerop of the elevated reef as observed 
by Professors L. Agassiz and Shaler. Тһе 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, and including the Marquesas, there is 
nothing exposed but beach rock (Plates I., V.), 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 hiding the substratum 
(Plate IL). Behind and upon this beach rock, æolian 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, 
