139 
Corresporulence — Mr. W. Gunn. 
Silurian rock exposed. The north side of Murton Pike forms the 
south side of the Gill here, and is almost entirely Silurian rock ; 
indeed, the west side of this Pike is wholly Silurian up to its suru- 
mit. Next, further up the Gill, is the Old Red Sandstone. Then 
still higher up occur the escarpments of the alternating limestones, 
sandstones, and shales of the Carboniferous series, including the 
Melmerby Scar Limestone, which is the thickest bed of limestoue on 
this part of the chain. Above this series, at the head of the Gill, we 
come to the Whin Sill, where a considerable quantity of its debris 
lies at its foot. More Carboniferous rocks take on above the Whin 
Sill, and slope backward each way to form the summit of the ridge 
on the north and south sides of the Nick. As to the thickness of 
the strata from the base of the Carboniferous rocks, in this section, 
to the bottom of the Whin Sill, I cannot do more than give a pro- 
bable estimate, and will venture to put it down at about 1000 feet. 
Should this thickness be near the truth, as I expect it may, and if 
the same thickness, or nearly so, occurs from the base of the Car- 
boniferous rocks to the bottom of the Whin Sill, at the old Pencil 
Mill, then, I think it may be fairly concluded that, the Silurian-like 
shale, at this place, is not real Silurian, but indurated carboniferous 
shale, and, therefore, the base of the Carboniferous rocks must be 
considerably below the bottom of the valley of the Tees at either 
Falcon Clints or the old Pencil Mill. The section at High Force, 
about two miles further down the Tees from this place, affords 
additional evidence, corroborative of the soundness of the conclusion, 
that the base of the Carboniferous rocks cannot be seen in Teesdale. 
1 may here refer Mr. Dakyns, or any of your readers, to that brief 
abstract of a paper on this section, by C. T. Clough, Esq., B.A., 
F.G.S., in the Geological Magazine for October, 1876, page 474. 
Before leaving the subject, I may, however, state that there is a 
possibility of some peculiar positions of the strata, such as a great 
upward bend, or the upcast of a considerable dislocation, bringing 
the base of the rocks in question to view. The Burtree Ford dyke 
bas a course nearly north and south ; it ranges up the east Allen to 
the west of Allenheads, thence through Weardale, at Burtree Ford ; 
and Mr. Förster, in his section of the strata, states that it crosses the 
Tees at Cronkley Sears. In Weardale this dyke brings rocks up 
to view, which would not have been seen, had the dyke not existed. 
There is some probability that it might produce a similar effect 
where it crosses through Teesdale ; but whether it does so or not, 
will be known by those who are better acquainted with the rocks 
in that part of Teesdale than I am. John Curry. 
Boltsburn, Eastgate, Darlington, 
February öth, 1877. 
IS THERE A BASE TO THE CARBONIFEROUS ROCKS IN TEESDALE? 
Sir, — M y friend Mr. Dakyns, in the last Number of your Magazize, 
asks the question, “ Is there a base to the Carboniferous rocks in 
Teesdale?” Permit me, on behalf of my colleague Mr. Clough and 
for myself, to answer the question in the affirmative. We cannot 
