The dip of 24 ft/mi (feet per mile) is equal to an angle of dip of 0°16'. The steepest mapped dips, found in 

 Colquitt County, amount to 48 ft/mi or only 0°31'. Thus nowhere in the area discussed can dips be found 

 that would be apparent even if outcrops were available and exposures ideal. The great extent of the area 

 however permits considerable vertical change to occur due to these exceedingly gentle dips. 



An unconformity as indicated by paleontologic evidence occurs in the northeastern part of the Coastal 

 Plain where middle Eocene deposits lie on Cretaceous. The approximate areal extent of the unconformity 

 is shown on figures 10 and 12 and it is also shown on the sections in figures 21, 22, and 27. A block 

 uplift or tilting at the end of Cretaceous time may have raised the area above sea level and prevented 

 deposition of Paleocene and lower Eocene sediments. The areal extent of the unconformity in the sub- 

 surface agrees with the few available surface data. A geologic map by MacNeil (1947) shows that the Pa- 

 leocene is found at the surface only as far east as Houston County and that no exposures are found east 

 of the Ocmulgee River. This has generally been inferred to be caused by overlap. The subsurface data 

 now indicate that overlap occurs onl y in the downdip area and that a major unconformity separates the 

 Cretaceous from the overlying middle Eocene sediments. 



Unconformities are known in the Coastal Plain but except for the major one discussed above they are 

 usually difficult or impossible to recognize solely from study of well samples. Marine and continental 

 conditions are known to have alternated but such alternation is represented by sands for the continental 

 deposits and fossiliferous, glauconitic, phosphatic elastics and limestones for the marine deposits. 

 Weathered zones indicating a hiatus in sedimentation are not generally recognized in the study of well 

 cuttings but have to be inferred from other data. Unconformities at the tops of all the units that have been 

 mapped in this report are thus either known or inferred. These are in every case disconformities rather 

 than angular unconformities. 



From comparison of logs in the well-log report by Herrick, faults seemingly occur in Crisp County 

 between wells 155 and 390 (see fig. 22) and in Clay County between wells 402 and 435 (see fig. 26.) The 

 fault in Crisp County has a vertical displacement of about 40 feet in the Tertiary beds. Figure 22 suggests 

 that in Crisp County a vertical displacement of about 90 feet may have occurred and that in early Tertiary or 

 pre-Tertiary time displacement may have been about 400 feet. Other faults may occur in the Coastal 

 Plain but the distance between the logged wells is so great that differences in elevation of formational 

 tops are more easily explained by gentle dips rather than by faults. Later work may possibly reveal 

 structure that is impossible to determine with available data. 



57 



