344 Proceedings of the Royal iSocieti/ of Victoria. 



Now, if it be remembered tliat the strata are ordinarily nearly 

 vertical, and that the crosscourses are usually nearly vertical, it 

 will easily be seen that the recorded throws are quite inadequate 

 to produce the recorded heaves. The figures recorded as 

 "apparent throw" seem to represent the actual vertical com- 

 ponent of the displacement, as measured by the ditierence of 

 level of the intersections of a i-ecognisable vein with the indicator 

 on the two sides of the crosscourse. Also, if the strata were 

 actually vertical, a crosscourse, whatever its inclination, would 

 necessarily produce a heave towards the smaller angle in plan if 

 the real movement were a downward movement of the hanging 

 wall in the direction of the dip of the crosscourse. (See Fig. 2). 



If the strata were not quite vertical with the same movement 

 the heave would at first diminish till it disappeared, and with a 

 further departure of the strata from the vertical, would become 

 an apparent heave in the opposite dii'ection. 



If the strikes of strata and crosscourse make an angle of 60° 

 with one another, strata with a dip equal to that of the cross- 

 course would be heaved towards the greatei- angle to the same 

 amount as vertical strata would be heaved toward the smaller 

 angle in plan. 



From these facts we must conclude that the movement has not 

 been a downward movement of the hanging wall side in tlie line 

 of dip of the crosscourse. The vertical component of the move- 

 ment is indeed, at least usually, downward on the hanging wall 

 side ; but it does not even approximately represent the whole 

 actual movement. The description of the crosscourses as normal 

 faults is therefore not incorrect, but is certainly quite inadequate. 



Ft is possible that this is the reason why the term " apparent 

 throw" is used in Mr. Lidgey's report. The alternatives of 

 incorrect correlation of the strata, undetected repetition, or 

 exceptional dips are quite out of the question. They could not 

 explain a consistent feature of so many crosscourses throughout 

 the field. 



The "apparent throw," then, represents the actual vertical 

 component of tlie displacement. The " apparent heave " is, 

 however, composed of two parts, one of which, relatively small, 

 is consequent on this vertical movement, and the other, relatively 

 large and usually in the opposite direction, is due to an actual 

 liorizontal component of the displacement on the fault. 



