which form the opposite Walls of Cross-veins 381 
Neither will it require much inspection to see that it does 
not signify whether the motion op be vertical or diagonal ; 
for a heave must of necessity take place whenever the lines of 
motion and of dip do not correspond : and this being the case, 
the greater the extent of elevation or subsidence, the greater 
will be the distance of the heave. 
On the other hand, it is equally clear that if the lode be 
perfectly straight, and the lines of motion of the mass and 
dip of the lode coincide, as in 7 s, the amount of the motion 
is immaterial ; for whatever it may be, no heave can possibly 
take place so long as this correspondence continues. 
Let us now examine a case in which the dip of the lode shall 
be irregular, and see what should be the direction of the mo- 
tion which would occasion simple intersections at some levels 
and heaves at others, but all the heaves in the same direction. 
Now it is evident, that with a vertical motion o p (Pl. IV. 
fig. 3), no very obliquely inclined vein can ever be simply 
intersected at one part of its downward course and heaved at 
another ; for if the direction of the dip remain the same, the 
direction of the movement tends to separate the severed 
portions at all parts of their descent. And the lower part of 
the elevated portion can be brought into contact with, or op- 
position to, the upper portion of the stationary one so as to 
cause a simple intersection, only by a change in the direction 
of the motion, or by reversing the dip of the lode. 
If, however, the dip be in opposite directions, in different 
parts of the lode’s descent, then not only may a vertical 
movement of the portion on one side of the fissure (or cross- 
vein) produce simple intersections at some depths and heaves 
at others, but the heaves at different levels may even be in op- 
posite directions; and this is of course the more likely to 
occur the closer the approach to parallelism between the dip 
of the lode and the direction of the motion. 
Let A B (Pl. IV. fig. 4) denote the original position of 
the surface, and ab é the lode in its original place, some parts 
of it dipping north, others south. Let A! B! be the present 
position of the surface which has been elevated from the level 
of AB, and a'b' 0d! the portion of the lode contained in the 
mass A' B'. Let it also be supposed that A! B! stands beyond 
AB, as well as above it; and that they are separated by a 
cross-vein: and also that the motion has been a vertical one 
from p too. ‘Then at the surface of A B the cross-vein will 
simply intersect the lode, and will continue to do so as far 
downward as b: from + to 6! the further or elevated portion 
will stand on the right of the unmoved one, and consequently 
from b to 6! the heave will be in that direction, although dif- 
fering in extent at different levels. As portions of the lode 
