Figure 24-2. Geologic cross section compiled from subsurface (well) data. 



in a direction up the dip. In this instance, the actual drilled interval is less than 

 the verticle depth of the datum bed. The effect is an apparently steepened dip 

 between the two wells. 



Unless a directional survey has been made, it is impossible to adjust the 

 log of a crooked hole to obtain a correct datum point. 



Dips or dips and strikes determined from cores can aid the subsurface 

 geologist greatly; but they can also lead him far astray in his interpretations. 

 It is hazardous to use core dips indiscriminately in subsurface mapping. The 

 core dips should always be adjusted by means of hole deviation or directional 

 surveys when available. When straight-hole determinations have not been made, 

 core dips should be used with caution. Figure 24-44 shows a straight hole 



A B 



Figure 24-3. Effects of crooked holes on datum elevations and interpreted dips. 



455 



