SOME NORTH-OF-ENGLAND DYKES. OAM 
of frequent occurrence, but which cannot very often be directly 
observed, viz. the vertical dying-out of the dyke beneath the strati- 
fied rocks. The whinstone was seen to terminate upwards very 
abruptly in the form of a low and somewhat irregular dome, over 
which the coal-measure shales passed without any fracture and 
only with a slight upward arching (fig. 1). 
West of this face and for a distance of about half a mile the dyke 
has been quarried, and its course is therefore marked by a deep 
trench. At one point it has been shifted laterally by a fault a little 
more than its own thickness. The next working-face is the largest 
one in the district. The width of the dyke at the time of our visit 
was 66 ft., and the depth of the working-face about 40 or 50 feet. 
Here the dyke was quite vertical. 
In the next quarry to the west, the width of the entrance was 
about 15 feet, and at the working-face, 170 yards further east, 29 feet. 
Here the dyke hades to the 8.8.W. at an angle of 70°. The adjacent 
rocks are shales and sandstones, and the zone of alteration extends 
to a distance of 20 or 30 yards. At the north side of the main 
dyke, near the entrance to this quarry, is a narrow dyke, about 4 
feet wide, of similar material. 
West of this point the dyke does not appear at the surface for 
some distance ; but Mr. Howell informed me that it has been proved 
in colliery workings ; and there can be no doubt that the dyke cross- 
ing Woodland Fell in an east-and-west direction, which can be traced 
to a point about 1 mile east of Middleton, is the same one. 
The above facts prove that the dyke in question varies very much 
in thickness both in a vertical and in a horizontal direction, that it 
frequently dies out before reaching the surface, and that it is lable 
to lateral shifts. Absence of continuity in the outcrop is thus seen 
to be no proof of a want of continuity underground. 
Until quite recently it has never been suspected that this remark- 
able dyke could be traced any further to the west than the neigh- 
bourhood of Middleton. The work of the Survey, however, has 
rendered it almost certain that the well-known dyke in the Eden 
valley, extending at intervals from the neighbourhood of Renwick to 
Armathwaite, is a portion of the same igneous outburst. 
Between the mest easterly exposure of the Hden-valley dyke and 
the most westerly exposure of the Cockfield dyke, near Middleton, 
no less than nine exposures, all lying very much in the same general 
direction, are now known. Mr. Howell was kind enough to mark 
these exposures on my maps, and I was thus enabled to visit two of 
them—one about 14 mile north-east of High Force Inn, where the 
dyke crosses the Bowles Beck, at the junction of two streams, and 
another about one mile south of Tyne Head, where it is also seen 
crossing a stream. In both these exposures the rock presents the 
macroscopic and microscopic peculiarities about to be described. 
From Bolam to the edge of the escarpment overlooking the 
Eden valley the dyke is intrusive in the various members of the 
Carboniferous formation. In the Hden valley it enters once more on 
Secondary ground. It has been traced by Renwick and Ruckcroft 
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