w- 



Figure 25-5. Stereogram of determination of true dip from two apparent dips. 



True Dip from Two Apparent Dips (2) 



This procedure has many applications (Nevin, 1949; Phillips, 1954). In 

 subsurface work, two cross sections may be drawn at an angle to each other in 

 order to intersect various oil wells. Neither section is at right angles to the strike 

 of the beds, so that both sections show only apparent dips. For example, in 

 Figure 25-5 one apparent dip is 35 degrees in a direction north 10 degrees east, 

 whereas the other is 25 degrees north, 80 degrees west. The apparent dips are 

 laid out on the stereographic net in their respective directions and marked by 

 dots, which lie on the projection of the great circle made by the bedding plane. 

 The stereogram is rotated until both dots lie on one of the meridional great 



536 



