48 On the Gulf Stream and the Keys of Florida. 
cleus around which cluster smaller fragments and coral sand ; 
the whole is then firmly cemented by carbonate of lime in solu- 
tion in the sea water, and the island thus formed is finally cov- 
ered with vegetation and inhabited by animals and man, The 
whole embryonic development, if I might use the expression, of 
coral islands may be observed upon the keys and reefs of Florida. 
On the outer or living reef a few have commenced to:form only 
a few years ago, and exist as yet only in the form of isolated 
boulders of dead coral, and not yet dignified with the name of 
keys. Others are formed of similar boulders, mingled with 
small ents, and coral sand, and firmly cemented by car- 
bonate of lime; but the large boulders are still conspicuous above 
the surrounding land, though immovably fixed. Still others are 
so covered with coral sand that the boulders are not observable, 
except by excavation or by examination of the outermost por- 
tion of the island towards the sea. The coral sand is always 
affected with the cross and oblique stratification so common in 
materials exposed to the violent action of the waves. All the 
islands on the outer reef are very small, of very recent origin, 
(some only a few years old,) and, therefore, as yet entirely barren. 
e examination of the larger and older inhabited islands of 
the line of keys prove beyond question that they have been 
formed in a similar manner. We have here also the same coral 
boulders, mingled with smaller fragments and coral sand, and the 
whole firmly cemented into solid rock, the same cross and oblique 
stratification indicating the former action of waves on an expose 
shore. e boulders here also sometimes stand above the sur- 
rounding cement exposed in their superior portions, as at Key 
Vaca; and at others completely covered with coral sand, as at 
Key West, and most other keys. This exposure of the | 
boulders above the surrounding cement in which they are. firmly 
fixed led Tuomey into the error of supposing that they were the 
ominent points of the original reef, elevated above the sea level 
Y igneous agency, and that the keys were formed by igneous 
by aqueous agency. That such is not the case is 
proved by more attentive examination and comparison with the 
smaller keys of the outer reef. There can be no doubt, there- 
