60 
FLORIDA GEOLOGICAL SURVEY. 
West, excepting, perhaps, that the cross-stratification is here 
more prominent, the strata dipping more frequently in 
several directions within the .same extent.” 
Notwithstanding the considerable elevation which the 
rocks along the mainland attain in the vicinity of Miami, 
Agassiz was of the view that these rocks, like the rocks of 
the Keys, had been built above water level by the action 
of winds and tides. He says on page 156: 
“We are satisfied that as far as coral formations have been 
observed upon the main-land of Florida and within the pres¬ 
ent extent of the coral reefs, no change of the relative level 
has taken place either by subsidence or upheavel of the coral 
ground, and that all the modifications which the reef has pre¬ 
sented at successive periods have been the natural conse¬ 
quence of the growth of reef-building corals, with the subse¬ 
quent accumulation of their products, in the manner described 
above.” 
The conclusions of Agassiz with regard to the gradual 
growth of the peninsula through the agency of corals 
have given rise to much discussion. On page 157 of this 
publication he says: 
“There we have a peninsula—a narrow, flat strip of land, 
projecting for about five degrees from the mainland, between 
the Atlantic ocean and the Gulf of Mexico, and forming an 
effective barrier between the waters of the two seas, which 
otherwise, even by the change of a few feet in the relative level 
of the intervening peninsula, would communicate freely with 
one another; and this peninsula we now know to have been 
added to the continent, step by step, in a southerly direction. 
“We know that the time can not be far behind us when the 
present reef, with its few keys, did not exist, and when the 
channel, therefore, was broader, and the Gulf Stream flowed 
directly along the main range of keys. We know further, 
that at some earlier period the keys themselves were not yet 
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 mainland, and that 
there was then nothing to impede a free communication be¬ 
tween the Gulf of Mexico and the Atlantic ocean. The chan¬ 
nel of the Gulf Streaija was not only wider—it was also less 
shallow along its northern borders, for the whole extent of 
