Mr. Hopkins’s Abstract of his Memoir on Physical Geoiogy. 229 
mineral vein and the fault are not to be referred to the same 
mechanical origin, or that other veins in the same district 
should not be referred to the same cause as such an one as that 
just described, from which, except where the above-mentioned 
difference of level becomes great, they differ in no respect. 
It is also highly important to observe, that (as far as investi- 
gation has yet proceeded,) where faults and mineral veins co- 
exist in the same district, they follow, with reference to their 
positions, precisely the same laws. 
I do not mean, however, to maintain that all mineral veins 
are necessarily to be referred to the same mechanical cause. 
I conceive that some of the Cornish veins—those, for instance, 
of St. Austle Moor—are clearly referrible to some cause quite 
distinct from that in which the veins of our limestone districts 
have originated. The latter possess, I believe, universally the 
characters which lead us to regard them as having originated, 
like faults, in dislocations produced by mechanical violence, 
while the former are almost totally destitute of these charac- 
ters. It would, therefore, be absurd to conclude that these 
two classes of veins have necessarily had the same origin. It 
is not, however, from d@ priori considerations that these points 
are to be finally decided: but since the evidence of dislocation 
afforded by a fault is independent of its vertical magnitude, 
I cannot but regard the mineral veins of our limestone di- 
stricts as indicative of dislocations in the masses in which 
they exist, equally with the faults with which they are so fre- 
quently associated. I therefore regard them in this point of 
view; the correctness of our doing so must, of course, be ul- 
timately tested by the harmony which may exist between our 
theoretical deductions involving this hypothesis, and the phz- 
nomena which these veins actually present to us. 
The planes of these dislocations approximate, in the first 
place, to verticality ; and, secondly, their horizontal directions 
bear distinct relations to the general configuration of the 
elevated district in which they exist. If there be a central 
axis of elevation, the directions of dislocation are approxi- 
mately parallel or perpendicular to it, as is the case in most 
of our mining districts; and if there be a central point of ele- 
vation, these directions diverge from it as a centre. Such 
appears to be the case in Mount Etna, and the groups of the 
Cantal and Mont Dor. The lake district in this country pro- 
bably affords a similar instance. 
These are the laws established by observation, so far as 
it has yet extended. Many anomalous cases may possibly 
exist, but they will not invalidate the conclusion, that, so far 
as the phenomena are characterized by these laws, they are 
