348 Proceedings of the Royal Society of Victoria. 



construction will apply equally to a bed or to an older fault-line]. 

 The arrows on the lines of strike represent direction of dip ; 

 those alongside other lines represent the direction of inclination 

 of the inclined lines, which these lines on the plan represent. 



ON drawn at right angles to OF is the projection on the 

 horizontal plane of the line of dip of the fault. 



01 may be thus ascertained : Take a point B on OF, and 

 make angles OB A, OBC, equal to the angles which the fault and 

 the lode respectively make with the vertical. Then in a height OB 

 the fault and lode will move in the directions of their dips to 

 distances measured on a horizontal plane by OA and OC 

 respectively. Draw lines (shown by dotted lines in Fig. 1) 

 parallel to OF and OD, and at distances from them equal to OA, 

 OC respectively. Their intersection is a point on the intersection 

 of the lode and fault, which can be then at once drawn. If 

 there is no rotation round an axis perpendicular to the plane of 

 the fault, the dip and strike of the lode beyond the fault should 

 be unaltered (neglecting any bending due to the movement, as is 

 done here throughout), RJ is therefore parallel to 01. If there 

 has been rotation, RJ needs to be plotted independently. 



Then, since RJ represents all points on the intersection of the 

 fault and the lode beyond the fault, the point once in contact 

 with O must have moved to some point represented in plan on 

 the line RJ. 



If the movement has been down the line of dip, this point 

 will be given by M (on the line ON), otherwise it may be at 

 some other point such as Q. OQ represents, on plan, the 

 movement of the point once in contact with O. 



To determine Q. : On the crosscourses at Ballarat East it is 

 often possible to ascertain directly the difference of level of the 

 points at which some recognisable vein crosses the indicator on 

 the two sides of the crosscourse. This is the true throw or 

 vertical component of the movement. If OB be taken equal to 

 this throw, then OA represents the amount of displacement on 

 plan in the direction of the dip, and if AQ be drawn parallel to 

 OR to meet RJ in Q, the true movement is thus determined as a 

 true thfow = OB, and a true lateral displacement = AQ. Fig. 1 

 sliows a general case; Fig. 2, the particular case of a vertical lode 

 or bed. Fig. 2 represents the case at Ballarat East, and it 



