38 FLORIDA REEFS. 
formed, and that then the channel between Cuba and Florida was wider 
still, washing freely over the grounds now known as the mud flats, between 
the keys and the main-land, and that there was then nothing to impede 
a free communication between the Gulf of Mexico and the Atlantic Ocean. 
The channel of the Gulf Stream was not only wider, — it was also less shal- 
low along its northern borders ; for the whole extent of soundings south of 
the main-land of Florida was an uncovered coral ground, upon which the 
deep-water species were just beginning to spread. But we may trace tlie 
change farther. There was a time when neither the southern bluffs of 
the continent, nor Long Key within the Everglades, nor even the Ever- 
glades themselves, existed ; when, therefore, the Gulf Stream had a broad 
communication with the Atlantic, and the southern shores of the United 
States extended in almost unbroken contiguity from west to east, from the 
shores of Texas and Louisiana to St. Augustine. At that time the gulf-chan- 
nel was, in reality, a broad bay, as broad as the gulf itself, destitute of all 
those obstructions which now cause the tropical current to follow such a cir- 
cuitous course between the West India Islands, through the Caribbean Seas, 
and around the peninsula of Florida. The influence which the Gulf Stream 
has upon the climate of the Atlantic is so well known that its connection 
with the changes which the current itself has undergone within a compara- 
tively recent period cannot be overlooked. If it is true, as we have every 
reason to believe, that the temperature of the Gulf Stream, in connection 
with the temperature of the southwesterly winds blowing obliquely across 
the Atlantic, modifies that of the western coast of EurojDC ; if it is true 
that the Gulf Stream and the southwest winds have an influence in determin- 
ing the course of the isothermal lines upon tiie two sides of the Atlantic, 
and of raising beyond their normal altitude the mean annual temperatures 
of northwest Europe, — then we may look to the physical changes which have 
occurred on the southeastern extremity of the North American continent 
for the cause — or at least a partial cause — of those changes of temperature 
which have taken place, in the beginning of the present period, in those 
very northwestern portions of Europe which are now so much warmer than 
the corresponding latitudes on the American continent, and which, soon 
after the accumulation of the glacial drift, had as low mean annual tem- 
peratures as the coasts of Labrador, Nova Scotia, and New England in 
our day. 
