SECOND ANNUAL REPORT—GENERAE GEOEOGIC HISTORY. 
167 
peninsula from Tampa northward nearly to the Apalachicola River 
may have been out of water. This is inferred from the fact that the 
surface formations in that region are Oligocene. However, it is pos¬ 
sible that the absence of marine Pliocene beds is due to post-PIiocene 
erosion rather than to non-deposition. 
During the Pliocene there was extensive deposition of the non¬ 
marine beds which are known as the Bone Valley gravel (“land pebble 
phosphates”) and the Lafayette formation. The conditions which 
permitted the deposition of these formations appear to have been low 
altitude of the land and the consequent accumulation of the products 
of mature weathering followed by an increase in altitude which stimu¬ 
lated erosion and caused the streams to remove, assort, and redeposit 
these weathered materials in their present position. That there was 
complete weathering of the rocks from which the materials of the 
Bone Valley and Lafayette formations were derived is shown by the 
fact that these formations contain the comparatively insoluble phos¬ 
phate of lime, left by the solution of the limestones, and the sands and 
clays which are the results of the decomposition of other rocks and 
are not themselves subject to further weathering. The accumulation 
of such large quantities of residual products must have taken place 
under conditions which did not permit of their ready removal, and 
such conditions would be most likely to be low altitude which accom¬ 
panied the Pliocene submergence, together with abundant heat and 
moisture. 
After the accumulation of the weathered materials, an increase in 
altitude was necessary to permit their removal and deposition in their 
present positions. Evidence of the stream action is found in the poor 
assortment of both the Bone Valley and Lafayette formations and the 
cross-bedding of the sands and gravels of the latter. The increase in 
altitude appears to have been most marked at some distance from the 
coast, for the clays, sands and gravels which make up these forma¬ 
tions would have been transported to the sea if the increase had been 
uniform. 
Following the deposition of the Pliocene there was an emergence 
of the land which not only included the greater part of the present 
surface of the State, but probably included a portion of the area which 
is now submerged. This emergence is regarded as the beginning of 
the Pleistocene, though it might with equal propriety be regarded as 
the closing epoch of the Pliocene. This emergence gave the streams 
erosive power, and caused extensive dissection of the Pliocene and 
older formations. It was during this period of erosion that the major 
features of the present topography were produced. Concerning the 
extent of the emergence there is considerable diversity of opinion; and 
