Correspondence — Mr. W. H. Dalton. 333 



Suppose two apparent dips, 41° N.W. and 33° N., 30° E. 



Result 441° N. 18° W. 



Draw B A, B Ciu the directions of the apparent dips : erect B B, 

 B E vertical to B A, B C respectively, and equal to each other. From 

 D, E, draw B A, E C, making BAB, B C E equal to the apparent 

 angles whose direction is shown hj B A, B C respectively. Join 

 A C, and draw B F vertical to it. Draw B G parallel to A C, and 

 equal to B E: join F G. 



Then B F is the direction of the full dip and G F B its amount. 



Proof.—U ABChe placed horizontally and A B D, B G E, B F G, 

 vertically, X>, G, and E will coincide, and DA, G F, EC, and A G 

 will be in the plane of stratification giving the apparent angles at A 

 and G and the full dip at F. In practice the triangle B G F might be 

 more expeditiously constructed between B F and A G. 



Problem 3. — Given a plane's dip and direction, to ascertain the 

 effect on it of a secondary tilt of known amount and direction, and 



three apparent dips, which may be taken two and two, thereby proving whether or 

 no the stratum is a true plane, and if not, the mean of the three results will indicate 

 the general dip. 



