Figure 24-8 is constructed solely on data supplied by the 24 wells that penetrated 

 the Paleozoic formations below the Jurassic unconformity. The block diagram 

 shows four of these wells, three of which are in the vertical planes of the block. 



In the central part of the Cambrian structure map, the actual datum, which 

 is the top of the Cambrian, has been destroyed by pre- Jurassic erosion. This is 

 shown by the fact that wells 8, 10, 16, 18, and 19 entered the Cambrian directly 

 beneath the Jurassic without first penetrating the systems that overlie the Cam- 

 brian toward the edges of the map. Although the contours within this area of 

 truncation are drawn to the elevations at which the Cambrian is encountered 

 below the unconformity, they do not represent the true structural configuration 

 of the strata. In order to do so, it would be necessary to reconstruct the original 

 thickness of Cambrian throughout the area of truncation and raise the elevations 

 accordingly. Even this process cannot be employed in the center of the area 

 where Cambrian beds are absent, for there is no method by which the depth of 

 erosion of the pre-Cambrian rocks can be determined. Close approximations can 



B 

 Figure 24-6. Typical eroded anticline involving a major unconformity in subsurface. 



458 



