138 ORIGIN AND DEVELOPMENT OP OPE DEPOSITS. 



that portions of the earth's crust have actually descended towards 

 its centre. The general idea among practical men in the West 

 of England, at anyrate among the comparatively few who believe 

 in rock-movements at all, is that the lodes are " heaved" horizon- 

 tally so many fathoms to the right or left, as the case may be. 

 This, of course, is true in a sense ; obviously, the descent of the 

 hanging-wall of an inclined fissure involves both vertical and 

 horizontal transference, and includes more or less of these 

 components respectively, according to the amount of inclination. 

 A great many illustrations of such heaves are given in works on 

 Physical Geology. A few examples will suffice in this place. 

 Fig. 9a, Plate X, represents a cross-section of a portion of country- 

 rock traversed by a lode-fissure cc, and subsequently fractured 

 as at dd. If now the fissure d becomes faulted by the descent of 

 the hanging-wall, as in fig. 9b, the lode cc will be faulted as 

 shewn. Plainly this may be spoken of as a downthrow of the 

 portion E or an upthrow of the portion E, but all experience 

 shews, when the matter can be brought to the test in other ways, 

 that it is really a descent of the part E, in the immense majority 

 of cases. If, indeed, the descent were sudden and abrupt, so 

 that we could see the upper portion of E standing, like a cliff, 

 above the surface of E, few would doubt the subsidence of E, 

 none could doubt the actual motion of the rock-mass ; but 

 generally we only see such faults long after their origin, when 

 the ground has been worn away at the surface, as shewn by the 

 dotted line xx in the same figure. 



In some cases the same fault, in heaving two lodes, throws 

 one to the right and the other to the left, as in the well-known 

 example at East Pool Mine, illustrated in fig. 10, in the same 

 plate, where aa bb represent cross-sections of two lodes dipping 

 in different directions. If now these be traversed by a cross- 

 lode, suppose in the plane of the paper, and if the front portion 

 be supposed faulted down to gg, as indicated by the dotted lines, 

 then cc will be a left hand heave, and dd a right hand heave to 

 anyone approaching from behind along a or b respectively. 



Drag of faults. The movement of extensive rock-masses 

 must necessarily produce many minor flexures and contortions in 

 the immediate neighbourhood of the fissure. Such phenomena 

 are well known under the term ' ' drag." They are naturally most 



