Geology of High Teesdale. 183 
of the Lune, near Lonton, have hardly produced any perceptible 
change in the texture of the contiguous rocks. 
Combining all thesé facts together, I do not hesitate to con- 
clude, that many of the mineralogical phenomena above-mentioned, 
are to be accounted for exclusively by the chemical action of 
the trap upon the contiguous beds of the metalliferous formation. 
If there were any doubt about the justness of the preceding 
conclusion, it is, I think, set at rest by examining the effects 
produced by trap dykes upon beds of the same general charac- 
ter with those in High Teesdale. In the case of certain dykes, 
the fact of a chemical change produced by the action of the up- 
filling trap upon the contiguous edges of the strata, is proved 
by evidence which amounts to demonstration. For a detail of 
some of this evidence, I must refer to my preceding paper 
(supra, p. 35, &c.) 
I think the University fortunate, in possessing a beautiful 
series of specimens, derived from beds in contact with trap dykes 
in the Isle of Anglesea. Those which Professor Henslow brought 
from the side of the Plas-Newydd dyke, not only resemble, but 
are almost identical with many of the specimens which I found 
near the Whin-Stll in High Teesdale. Now the Anglesea spe- 
cimens are taken from nearly horizontal beds of limestone, slate- 
clay, &c. which abut against a vertical dyke of trap filling up 
a chasm in the strata. Whatever may have been its origin, it 
must have been formed after all the horizontal strata were depo- 
sited; and as those portions which abut against the dyke are 
changed in texture, but gradually, at some distance from it, recover 
their character, the change can only be ascribed to the action of 
the trap*. If then we be allowed to argue from similarity of 
* For all details on this subject, I must refer to Professor Henslow’s Paper in the 
preceding Volume, p. 401—424. 
Analogous 
action of Trap 
Dykes. 
