SECOND ANNUAL REPORT—GENERAL GEOLOGIC HISTORY. 
171 
the cycle of submergence there was a large addition to the detrital 
surface materials in the form of coarse-grained, white sand. The ex¬ 
tent of the submergence is undetermined, but it probably covered the 
major portion of the surface which lies below the 100-foot contour, 
and it is possible that the submerged tract was somewhat greater. 
The submergence was of short duration, and was followed by an 
emergence which was sufficient to expose an area somewhat beyond 
the present margin of the State. In discussing the physical changes, 
it has hitherto been necessary to mention only the broad changes, be¬ 
cause the details of successive movements have not been recognized, 
but in the case of the Pleistocene submergence certain minor details 
have been preserved. These are in the form of marine terraces which 
represent periods when the relation between the land and sea remained 
uniform long enough to permit their formation. (See Fig. 2, Plate 
VI.) The most pronounced terrace observed during the recent field 
season is about twenty-five feet above sea level, but there is at least 
one -and perhaps more at higher levels. It »is to be hoped that the 
completion of topographic surveys similar to those in other States of 
the Coastal Plain will enable the geologist to discriminate these ter¬ 
races ; but at present the absence of satisfactory contour maps makes 
their study impracticable. 
The slight submergence which has taken place in comparatively 
recent times has permitted the sea to enter the lower portions of the 
stream valleys and has covered a narrow belt of land along the entire 
coast. The small submerged valleys along the west coast were doubt¬ 
less carved during the uplift just preceding this submergence. That 
the movements which have taken place have not always affected the 
entire State uniformly appears probable, and this recent submergence 
of valleys on the west coast has been regarded as an example of un¬ 
equal movement. The following statement by Dali 1 illustrates one of 
the views which has gained wide credence: 
The mapping out of the distribution of the different geological horizons 
from many isolated observations, a good number of which were by Mr. Willcox 
himself, as shown on the map in Part II, taken into consideration with the 
observation of Shaler and others on the east coast, indicated that the peninsula 
of Florida has experienced a tilting by which the eastern margin has been ele¬ 
vated between twenty and thirty feet, while the western coast has been depressed 
about the same amount. This tilting is supposed to have taken place since the 
Pliocene. To the data of 1891, upon which the above generalization was based, 
Mr. Willcox has lately added observations which still further emphasize the fact. 
He finds that, off the streams falling into the Gulf of Mexico from the peninsula 
in the relatively shallow waters over the submerged plateau to the west, chan- 
1 Dali, W. H., Tertiary Fauna of Florida. Trans. Wagner Free Inst, of 
Sci., vol. iii, pt. vi, 1903, p. 1544. 
