362 Mr. Hopkins’s Abstract of his Memoir on Physical Geology. 
It is also important to remark, that the accurate coincidence 
above spoken of will require two coexisting systems of joints 
to be at right angles to each other, since such is the law recog- 
nised in lines of dislocation. Observation, however, so far as 
it has proceeded, appears in many instances, I believe, to con- 
tradict this law in the directions of joints. Should any other 
laws be established hereafter, or very frequent deviations from 
the one just mentioned, it will probably be found necessary to 
abandon altogether the notion that lines of dislocation have 
been principally determined by the directions of joints, rather - 
than by the mode of action of the elevatory force. 
The theory which it has been the object of my memoir to 
develope, enables us to account for nearly all the more im- 
portant phenomena of elevation; but before we finally decide 
on its relative claims to our adoption, we are manifestly called 
upon to remove as far as possible, by accurate observation, 
the uncertainty which still remains respecting the possible in- 
fluence of a jointed structure in producing what I have termed 
the primary phzenomena of elevation. ‘These speculations are 
thrown out with the hope of indicating some of the more cri- 
tical points of inquiry on which the ultimate determination of 
this question must turn, and which are generally best indicated 
in such cases by theoretical discussion. The necessary re- 
lations which I have shown must exist, according to one of 
these theories, between the directions of dislocation and the 
general, and in some cases local, conformation of the elevated 
mass, will probably do much towards enabling us ultimately 
to decide between them; and it is therefore of the first im- 
portance that the observer who may hereafter wish to eluci- 
date this subject, should remark these relations as carefully as 
those which may exist between the dislocations themselves, or 
the joints with which they may be associated *. 
We may here observe, that the only difference between the 
two theories we have considered, consists in the cause which 
they assign for what I have termed, with reference to the 
* It would be important, as before intimated, to observe the directions 
of joints in a conical elevation with lines of dislocation diverging from its 
vertex. [am not aware that the existence of a similarly diverging system 
of joints has ever been suspected. It would also be highly desirable to ob- 
serve whether there be any continuity in the joints of two contiguous but 
distinct formations, and particularly when one formation is primary and the 
other. sedimentary. The perfect continuity of the veins in Cornwall, in 
passing from the killas to the granite, forms a curious feature in the geology 
of that district, if we are to regard the former as a sedimentary deposit. 
In such case, it would clearly demonstrate that the regular structure to 
which, I conceive, many of those veins must be referred, was superinduced 
in that district after the great dislocations which must have accompanied 
the injection of the granite. 
