Faulting at Ballarat East. 351 



of intersection and the direction of movement make only a small 

 angle with one another. 



The direction of striations, if sufficiently decisive, may be used 

 to determine the direction of movement — determining the ratio 

 of OB to AQ. 



The diagram on a horizontal plane is especially useful in 

 working lodes ; as DO, OR, RE usually represent actual drives, 

 and the line of intersection is sometimes ascertained by the 

 positions of lode and fault at a lower level. 



Plans on the plane of the fault may also be used, and are 

 chiefly convenient as showing at once on the diagram the angle 

 which the striations should make with the horizontal line in the 

 fault, and for the ease with which they deal with rotations, 

 though Mr. P. Lake, who uses this construction to ascertain the 

 true movement on a fault (Geol. Mag. 1897) states that in the 

 case of a rotation the problem is insoluble. 



Figs. 5 to 8 illustrate such diagrams. 



OF is a horizontal line in the fault-plane. 

 OH, RL are traces of the planes of the lode on the fault- 

 plane. 

 OP is the direction and amount of movement. 



In Fig. 5, OD, 01, drawn as on a horizontal plane with OF, 

 represent the strike of the lode and the projection of its line of 

 intersection. 



IG is drawn perpendicular to OF, FI making angle GFI equal 

 to the inclination of the fault to the vertical, GH = IF. Then OH 

 is determined. In the absence of rotation RL is parallel to OH. 



If, however, it is found that on passing the fault the trace of 

 otherwise parallel bedding planes is altered from OH to OK, thig 

 rotation, due to movement on the fault, will affect also to the 

 same amount lodes, etc., crossing these beds. A lode, whose trace 

 on this side of the fault was parallel to PT (Fig. 6) will be 

 turned to Pr. 



The true movement is ascertainable as before. Fig. 5 repre- 

 sents the case of a horizontal recognisable vein crossing the bed, 

 represented by OH. UV evidently represents the actual move- 

 ment, and is easily resolved into two components as before. 



Fig. 7 represents two non-parallel lodes. OH, Oh, the 

 directions of their traces on this side of the fault OR, Or, the 



