BASALTIC ROCKS, DYKES, MINERAL VEINS, &c. 77 
altered portions of stratified rock, and appears geographically related 
to certain great basaltic dykes. It is traversed, like all the beds of 
the limestone series, by mineral veins, sparry fissures, and common 
faults. The rocks above and below it are (locally) metamorphic. It 
is frequently columnar, and impresses a like structure on some of 
the beds in contact with it. 
The geological place of the Whin sill is better known in Teesdale, 
round Cross fell, and along the western edge of the Penine chain from 
Brough northwards, than elsewhere. From my own inspection, and 
the statements of miners, I can not doubt that the place of the Whin 
sill, in Teesdale and Tynedale, and along the breast of the Penine 
chain, is constantly below, but not far below the Tyne bottom lime- 
stone, (which forms the upper part of the great scar limestone of Ingle- 
borough), and above the thick limestone of Melmerby scar. More 
than this can not be said, because of the variable nature of this part 
of the series of strata, the augmentation of its total thickness to the 
north, and the interposition of new limestones, gritstones, and shales, 
from Murton northwards. It is to this interpolation of new terms 
that the apparent discrepance of its position at Murton and Rundle 
beck is owing. This is easily seen by examining a sufficient number 
of points. It is distinctly seen in this relation, in Hilton beck, at 
High-cup-nick, in Knock Ore gill, Crowdundle beck, Troutsdale, Maize- 
beck, Teesdale, and Tynedale. It is from its stratiform character and 
constant position that the basaltic mass of Teesdale and Tynedale has 
received its name of ‘ Whin sill,’ in contradistinction to ‘ Whin dykes 
besides being thus definite in its leading relations to the limestones 
indicated, its surfaces are generally conformed to their planes of stra- 
tification. Of this the Holwick scars, the bed of the Tees near 
Winch bridge, the High force, and the whole western escarpment, 
appear to me to furnish decisive evidence. But yet there is some 
variation in this respect, especially in the cliffs which border the Tees 
below Caldron snout. In this locality, on the left bank of the Tees, 
the Whin sill appears in Widdybank scars, and, as Professor Sedgwick 
describes it, unconformably sweeps over the edges of some of the 
