256 DEEP BOREHOLE SURVEYS AND PROBLEMS 



The succeeding problems on boreholes not at right angles 

 to the strata strike appear to provide sufficient variant 

 forms of the above. Since in these cases we are dealing 

 with cores actually at the stratum or seam being sought, 

 our notation will have to be modified a little. 



INCLINED SINGLE BOREHOLES: METHODS OF OBTAINING DIP, 

 THICKNESS AND DIRECTION OF BEDS 



Vertical boreholes will always yield direct data for the 

 dip of the beds especially if they provide cores. Then the 

 dip is the maximum inclination shown by the bedding; 

 therefore we shall not deal with them but consider inclined 

 or meaned deviated boreholes. 



1. To Obtain the True Dip of Beds from a Borehole 

 Not at Right Angles to the Strike of the Bedding.^ — Here 

 four possible cases of borehole penetration arise in practice, 

 and each of these takes two forms according as the hole is 

 a dipper or a riser, as in Figs. 172 and 173 and Plate XV, as 

 follows : 



Case 1. — Where the beds dip or rise in the same direction 

 as the hole, but more steeply (Figs. 172, 173). 



Case 2. — Where the beds dip or rise in the same direction 

 as the hole, but less steeply, Case 2, Plate XV. 



Case 3. — Where the beds dip or rise in the opposite 

 direction to the hole and more steeply than a plane normal 

 to the plane through the drill hole and the strike of the beds. 

 Case 3, Plate XV. 



Case 4. — Where the beds dip or rise in the opposite direc- 

 tion to the hole and less steeply than a plane normal to 

 the plane through the drill hole and the strike of the beds. 

 Case 4, Plate XV. 



The general formula is most easily derived for the case 

 of a hole dipping in the same direction as the beds (Figs. 172, 

 173). 



1 White, E. E., Eng. Min. Jour.-Press, Vol. 98, No. 12, p. 524, or "Loca- 

 tion of Mineral Fields," p. 98, Crosby, Lockwood & Sons. 



