360 Mr. Hopkins’s Abstract of his Memoir on Physical Geology. 
[whether] these latter phanomena have exercised an influence 
in determining the positions of the joints, supposed to be sub- 
sequently formed in the elevated mass. Now, assuming the 
coincidence just mentioned, there must of course be the same 
relations between the general conformation of the elevated 
mass and the directions of joints, as those which have been 
already stated to exist between that conformation and lines of 
dislocation; and therefore, if we assume the prior existence 
of joints, and also that the lines or axes of elevation have been 
principally determined by the points of application of the ele- 
vatory force in the lower portion of the elevated mass, we must 
necessarily conclude, that some relation must exist between 
the causes which have produced the jointed structure, and the 
action of the elevatory force; 7. e. between the action of a force 
extraneous to the mass, and that internal molecular action, to 
which it would seem absolutely necessary to refer the formation 
of joints in the undisturbed mass. ‘To assert such relation to 
be physically impossible, would, in the present state of our 
knowledge, perhaps, be absurd; but it does appear to me that 
the difficulty of conceiving it is so great as to form a most se- 
rious, if not a fatal objection, to any theory in which it should 
be involved as a necessary consequence. To avoid this ob- 
jection, we might proceed on the hypothesis, that the lines or 
axes of elevation have been principally determined by the lines 
of less resistance along the joints, rather than as above sup- 
posed; and such might be the case, if the principal line of 
action of the elevatory force* should not deviate materially 
from either of the two directions at right angles to each other 
in which we are assuming joints to exist. If, however, that 
principal line should approximate to an angle of 45° with these 
rectangular directions, and should be of considerable length, 
the hypothesis would be, [ conceive, altogether inadmissible. 
Supposing then the accurate coincidence of the directions 
of joints and those of fracture to be hereafter established, it 
would appear that the hypothesis of the laws discoverable in 
lines of fracture being generally due to the prior existence of 
some regular structure in the undisturbed mass, would still 
involve serious difficulties, on account of the relations existing 
so generally between the lines of fracture and the configuration 
of the elevated mass, for which, with the above hypothesis, it 
* It must be recollected that we can only judge of the superficial form 
and dimensions of the mass to which the elevatory force has been applied, 
by those of the actual elevations. These appear unquestionably, I conceive, 
to justify the notion of sufficiently determinate lines of action of the ele- 
vatory force, at least in a sufficient number of instances to give due weight 
to the argument in the text. 
