Geology of High Teesdale. 181 
parts of it which are exposed, are, however, too crumbling and 
incoherent to be of any use in ornamental architecture. 
I have now detailed to the Society all the important facts Chemical action 
with which I became acquainted, during my examination of the oS eee 
physical structure of High Teesdale*. Of the mechanical agency 
of the trap, it appears to me, that we have, in two or three in- 
stances, a perfect demonstration. As far as regards its chemical 
action, some one may perhaps object, that the beds of granular 
limestone and hard shale are formations sui generis, which took 
place immediately before and after the deposition of the great 
Whin-Sill (General Section, No. 71.) and that they have not 
been modified by any external action subsequent to their original 
deposition. This theory not only leaves the mechanical action 
unaccounted for, but appears to involve the supposition, that 
the Whin-Sill must occupy a given place in a regular succession 
of strata, a supposition which is at direct variance with some of 
the facts described above, as will be seen at once by a comparison 
of the general section (supra, p. 8.) with the sections below Cal- 
dron Snout and White Force. 
If the granular limestone be independent of the trap, it 
might be expected to appear in other parts of the metalliferous 
formation where no trap is present ; but under such circumstances, 
it has never been met with. Again, if the hard and granular 
beds only indicate a natural alteration in the deposits immediately 
preceding the precipitation of the trap, we should naturally expect 
to find some analogy between the component elements of these 
beds, and of the trap. But I could discover no such analogy ; 
nor can I comprehend how a bed of pure granular limestone, 
* As I was accompanied in almost all my excursions by Mark Watson and J. Dent, 
two intelligent practical men well acquainted with the mineralogical features of the district; 
I venture to hope, that very few facts, connected with the objects of this paper, escaped 
my observation. 
