22 REPORT OF INVESTIGATIONS No. 50
The marine terrace deposits consist mostly of loose unsorted quartz sand with varying amounts of organic matter and occasional seams of clay. These sediments are generally thought to have been deposited during interglacial times of the Pleistocene ice age when sea level was higher than it is at present. Table 3 gives the altitude of the more prominent terraces as defined by Cooke. Only the Pamlico terrace with a shoreline at about 30 feet and the Wicomico terrace with a shoreline at about 100 feet are well developed in Orange County. The altitudes in Orange County above 100 feet represent eroded remnants of the higher Okefenokee and Coharie terraces or sand dunes formed during higher stands of the sea.
TABLE 3. ALTITUDES OF TERRACES IN FLORIDA.
Brandywine 270 feet Coharie 215 feet Sunderland 170 feet Wicomico 100 feet Penholoway 70 feet Talbot 42 feet Pamlico 25 eet Silver Bluff 5- feet
STRUCTURE
The surface-of the limestones of Eocene age is shown in figure 8. This represents approximately the land surface as it was in post-Eocene/pre-Miocene time after a long period during which the limestone was above sea level and exposed to erosion. Figure 8 is one interpretation of limited data, and future studies based on more complete information and regional interpretation may result in drastic revision. For example, a steep-walled trough is shown in the southeastern part of the county, whereas actually there may be a fault in the St. Johns River valley as indicated on the geologic section in figure 6.
Figure 7 shows contours on the top of the Avon Park Limestone. The top of the Avon Park Limestone appears smoother than the top of the overlying Ocala Group and was probably not eroded except where the Ocala is missing. Therefore, the Avon Park Limestone probably more nearly represents the regional dip of shallow limestone formations underlying Orange County.
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