138 The Flora and Fauna of the Florida Keys. — [March, 
tion of future visitors to this interesting region to several points 
in the mode of introduction of plants and animals into a new 
region, worthy of more extended study. 
e have here a curious example, on a very small scale to be 
sure, of land of comparatively recent origin, which has received 
its flora and fauna from two different and very distinct sources, 
the West Indies and the North American Continent, and, as it 
seems, the flora chiefly from the former, the fauna mostly from 
the latter. 
For a proper understanding of the subject I must refer to the 
description of the Florida keys and reefs, by Professor Agassiz, 
in the Coast Survey Report for 1851 (it was never published im 
extenso), and in his Methods of Study ; also to an able paper on 
the same subject, by the late Lieut. E. B. Hunt, of the United 
States Engineers, in the Coast Survey Report for 1862, and the 
American Journal of Science, vol. xxxv. 
Lieutenant Hunt expresses the opinion that the reefs and keys 
shoot out as it were by their western end into the deep waters of 
the Gulf of Mexico. He says, ‘“* The well-traced curve along 
which this grand Florida bank thrusts itself out into the deep 
waters of the gulf is strikingly significant of some continuous and: 
regular agency in its production. The adjacent flow of the Gulf 
Stream would most naturally be assumed to govern in some way 
the production of this curve. It however runs in the contrary 
direction to serve this explanatory use, and it is in fact rarely 
found to run close in upon the reef. There is, however, an eddy, 
countercurrent, intermitting in character and of variable rate, but 
on the whole a positive and prevailing current.” We have not, 
unfortunately, observations enough of the currents near the reef to 
confirm these remarks otherwise than by a few scattered and often 
contrary ones, but judging by the effects, the above statement 18 
undoubtedly true, and theoretically we should expect to find a 
countercurrent in the concave side of a bend of the main current. 
To the effect of this eddy ought to be added the still more regu- 
lar westward action of the trade-wind and the flood tide. The 
formation of new islands and the westward extension of the reef 
are, however, probably of more than secular slowness, and the 
first discoverers of what was then called The Martyrs found them 
very nearly as we see them now. We may even have to record 
riods of retrogression as we do in glaciers, when a period of : 
exceptionally frequent or violent hurricanes destroys more than 
the growth of corals and the piling up of their débris can supply: 3 
Reo 
