1070 



Subsurface Geologic Methods 



Contour interval =25 gammas 



Figure 563. Magnetic contours of same area shown in figure 562. Magnetic anomaly 

 is present at A but absent at B. Pre-Cambrian formation producing A anomaly 

 is 3,000 feet deeper at B. (After Coffin. Reproduced permission Am. Assoc. 

 Petroleum Geologists.) 



