Mr. Hopkins’s Abstract of his Memoir on Physical Geoiogy. 359 
tion. Others more limited may be due to partial elevations. 
Where they are observed, the local configuration of the mass 
must be examined, and thence the directions of the conse- 
quent tensions superimposed on that of the general mass must 
be inferred. The equation of.page 273 will then determine the 
resulting directions of the fissures, and therefore the nature of 
the deviations. In simple cases, the remarks in page 276-277 
will enable us to do this with sufficient accuracy to compare 
the theoretical deduction with the observed pheenomena, 
V. It has already. been stated, that all consideration of 
those portions of the earth’s crust, in which a regularly jointed 
or laminated structure may have prevailed previous to their 
elevation, has been excluded from the investigations contained 
in my memoir, because I wished to keep them distinct. from 
any speculations respecting the operation of other causes than 
the one whose effects I proposed to develop. In our general 
speculations, however, on theories of elevation, it is necessary 
to consider how far these dislocations which, according to the 
theory I have been discussing, must be regarded as primary 
phenomena, areanything more than secondary ones, depending 
on lines of less resistance, produced by some such particular 
structure as that above mentioned. Much valuable informa- 
tion respecting joints may be expected from the forthcoming 
work of Professor Phillips on the Geology of Yorkshire; but 
at present we know but little accurately about this important 
feature in the structure of rocks, and of its cause, I conceive, 
absolutely nothing. We have, therefore, no positive reason 
to conclude that this peculiarity of structure has generally 
been superinduced after the elevation of the mass in which it 
exists, though in some cases there appears little doubt of 
such having been the fact. It is highly important, however, 
to determine whether any perfect coincidence does exist in 
the directions of dislocation, and of joints in the same district ; 
and it is to be hoped that geologists will direct their earnest 
attention to this subject. Should this coincidence be esta- 
blished generally in districts where the fractures are parallel 
and at right angles to each other, it will still be important to 
ascertain how far it exists in elevations approximating to the 
conical form ; and, in all cases, whether the directions of joints 
bear any relations to the configuration of the mass, as mo- 
dified by partial elevations. All these are points of interest 
which we may hope by accurate and careful observation to 
determine. Should the coincidence, however, between joints 
and lines of fracture be perfectly established, we shall still 
have to consider whether the joints, by their prior existence in 
the undisturbed mass, have determined the lines of fracture, or 
