358 Mr. Hopkins’s Abstract of his Memoir on Physical Geology. 
they are deducible by strict mechanical reasoning, appears to 
me, in the present state of our speculations and practical 
knowledge, to give to the theory 1 have been attempting to 
develop the strongest claim to the attention of geologists. 
It will be observed, that a most essential part of this theory 
consists in the relation which it assigns between the directions 
of dislocation and the general configuration of the elevated 
mass at the instant previous to its rupture. It may, at first 
sight, appear impossible to ascertain what this form may have 
been, now that we can only examine the mass in its dislocated 
state; but this difficulty, though it must always exist in a 
greater or less degree, will not appear so serious a practical 
one, when we consider that since necessary relations must 
exist between the form of the mass at the instant above men- 
tioned, and the lines of dislocation, and again between these 
lines and the actual disturbed form of the mass, some such 
relations must also exist between this latter and the previous 
form. Thus if the actual form be approximately conical, we 
may conclude it to have been also conical at the instant of 
dislocation; and if the disturbed district be of great length 
as compared with its width, and presents a well-defined axis 
of elevation, we may conclude the unbroken elevation to have 
been approximately cylindrical. Partial elevations which may 
have been superimposed upon a general one, as already de- 
scribed, at the instant previous to dislocation, must generally 
be more difficult to detect, since it*may frequently be impos- 
sible to distinguish present indications of them from similar 
elevations which may have been produced by the elevatory 
force entirely subsequently to the formation of the fissures. 
On such points the observer must of course exercise his dis- 
crimination and judgement. Deviations from rectilinearity or 
parallelism in the lines of dislocation are not to be regarded 
necessarily as anomalies. We frequently speak, it is true, of 
the law of parallelism in such phaenomena, as if that were 
their essential characteristic, but it is manifest that, according 
to our theory, this is only a secondary property in them, de- 
pending on the rectilinearity of the general axis of elevation. 
In conical elevations such as those before alluded to (p. 233) 
there is no approximation to parallelism in the observed fis- 
sures; and if the general axis of elevation be curvilinear, the 
longitudinal fissures preserving their parallelism with it (ac- 
cording to theory) will be also curvilinear, while the trans- 
verse fissures perpendicular to the former at their points of 
intersection will no longer be parallel. ‘These deviations from 
rectilinearity and parallelism are due to the action of the ge- 
neral elevatory force, and to the nature of the general eleva- 
