352 Proceedings of the Royal Society of Victoria. 



amount of their observed displacements along the fault. RP, 

 rP, the directions of their traces on the fault plane on the other 

 side. Then the true movement is given by OP. Mr. P. Lake 

 uses this construction for the displacement of an anticline. 

 Rotation presents no difficulty in liedded rocks, for its amount 

 is at once ascertainable, and if there had been observed displace- 

 ment to OS, OS, with a rotation represented by the angle SPR, 

 or sPr, the construction to fix P would be still as easily made. 



Fig. 8 represents a diagram to deduce the movement of a 

 point X from that of O, when there is rotation the line OX may 

 be supposed displaced parallel to itself to PZ, and then rotated 

 about P to PY, then XY will I'epresent the actual movement of 

 the point once in contact with X, the rotation remaining' the 

 same. 



Cases of alteration in shape of either block (as by a fault 

 meeting the first fault, or any other cause) need to be each 

 treated as suits the individual case. In the case of intersecting 

 faults it may be convenient to examine the movement along and 

 at right angles to their line of intersection. 



The complete description of the movement in a fault comprises 

 three parts — the throw, the true lateral displacement, and the 

 rotation. With a rotation, the throw and lateral displacements 

 will vary from point to point, and all may vary with an 

 alteration of shape of one block either gradually or suddenly. 



Formulae for calculation might be given for all these cases, 

 but the calculation would be usually more troublesome than the 

 diagram, and the diagram can be easily made as accurate as the 

 data themselves, on which a calculation would have to be based. 



A case is, perhaps, worth referring to which may occur, but 

 is scarcely a true case of faulting. It may happen that the 

 deposition of lode matter has gone on under .similar conditions in 

 two fractures meeting a fault from the two opposite sides. The 

 lodes produced may be similar; the fractures which they occupy 

 are independent, and there may be apparently throw, heave, or 

 rotation, whereas really there is only a similarity between two 

 distinct lodes occupying fractures which never have corresponded. 



The crosscourses of other fields have not been described with 

 the same detail as those of Ballarat East. It seems, hosvever, 

 that a similar oblique motion, as might be expected, is found in 



