MUSEUM OF COMPARATIVE ZOOLOGY. 141 
subject to energetic erosion have contributed their detritus to this basin. 
The line of the Antilles appears to me to mark the phenomena of coun- 
ter-thrust due to the accumulation of deposits off the coast of South 
America, much as the peninsulas of Florida and Yucatan mark the 
effects of sedimentation in that sea and in the Mexican Gulf. To the 
down-thrust caused by sediments derived from the island of Cuba, and 
deposited on the sea-floor to the northward, we may perhaps attribute 
the sudden termination of the Florida elevation on the south. The 
general tendency to counter-thrust uplift produced by the growth of 
strata in the Gulf of Mexico, and manifested in the peninsula of Flor- 
ida, is here interrupted by the process of local sedimentation. It is 
probable that, at the present time, the considerable energy with which 
the Gulf Stream moves through the Strait of Florida may hinder the 
process of deposition of sediment derived from the Cuban land mass ; 
but, as I shall endeavor to show in the sequel of this paper, this limita- 
tion of the Gulf Stream is probably a matter of very recent geologic 
time. 
Turning now again to the Cincinnati axis, let us note its relations to 
the geography of the district at the time when it was formed, to see what 
light it may throw upon the development of the curious elevations about 
the Gulf of Mexico and the Caribbean Sea. The Cincinnati axis, as is 
well known, is a singularly broad fold, which was developed on the floor 
of the palzeozoic sea at a distance of two hundred miles or more from the 
then shore of the Appalachian Islands, and generally parallel with the 
ancient land. At first, in the period of the Lower Trenton, this floor 
appears to have been tolerably level. Before and during this period in 
the history of the earth, a vast amount of detritus was borne from the 
Appalachian land, and deposited on the sea-floor near its eastern shores. 
Thus, along these old shores we had a vast thickness of sandstones of 
the Okoee and Chilowee age, and above them a great thickness of rocks 
belonging to the Knox group, which, though partly of organic origin, are 
largely composed of inorganic waste from the old lands on the east. 
There is no doubt that these last sediments were derived from the 
Appalachian land, and they form an extremely massive system of sedi- 
ments along the ancient shore. Following their onlaying, this portion 
of the sea-floor which they occupied sank to a great depth, as is shown 
by the peculiar character of the sediments and the organic forms in 
the Trenton rocks of Eastern Tennessee. Apparently at this time the 
Cincinnati anticlinal rose to near the surface of the waters, to a point 
where it exposed the bottom of the sea to the action of currents suffi- 
