C. T. Clough—The Whin Sill of Teesdale. 441 
Mr. B. N. Peach, also, of the Geological Survey, informs me that 
in the Stirlingshire Coal-field, the Whin Sill which crops out from 
Denny to the Abbey Craig at Stirling eats up near Denny the lowest 
limestone and several fathoms of other beds, for a distance of three 
or four miles. That these beds had not thinned out previous to the 
intrusion seems clear from the limestone passing into the trap above 
and emerging from beneath it about four miles north frum the 
place of disappearance, no limestone being found in the intermediate 
place. Figure 5 roughly represents the state of the case here. 
3—4 miles. 
Fic. 5.—Diagram of the Whin Sill from Denny to the Abbey Craig at Stirling. 
a. Limestone. b. Whin. 
There is some suspicion of the same kind of thing in the South 
Staffordshire Coal-field. The following passage occurs in Jukes’ 
memoir on this Coal-field, page 182 :—* I was assured also by almost 
every one engaged in the works of this neighbourhood that, notwith- 
standing the variation in thickness of the ‘green rock,’! there was 
no change in the total thickness of the measures ; that, for instance, 
the thickness between the New mine coal and the Blue flats ironstone 
remained the same, whatever might be the variation in the ‘green 
rock.’ In other words it was affirmed almost universally that the 
‘oreen rock’ not only intruded between the measures, but obliterated 
a mass of beds equal to its own thickness.” He then, however, 
goes on to show by various pit sections that this statement certainly 
does not hold good for all places, and apparently concludes that any 
truth there is in it may be explained, either by the squeeze of the 
measures having been greater the greater the thickness of the 
basalt, or by a partial thickening or thinning of the basalt having 
in places happened to coincide with the reverse in the other beds. 
The stratigraphical evidence, indeed, of the assimilation is so 
strong, and from so many different quarters, that I do not think it 
would be right to shut our eyes to it for fear of facing certain 
theoretical difficulties. 
The main difficulty which at first presents itself is the chemical 
one. It is objected that the Whin is of very uniform chemical 
composition throughout, but that the beds which are supposed to 
have been absorbed are of very various composition—that in one 
place you suppose a great mass of limestone to have been absorbed, 
and in another place a mass of sandstone, and yet there is no 
trace in either place of there being so much extra CaO or SiO, in 
1 <¢ Green Rock’’ is the local name for intrusive sheets of basalt in the South 
Staffordshire Coal-field. 
