30 Professor Sepawick on Trap Dykes 
slaty texture. These substances bear no resemblance either to 
the sound or decomposing specimens of the dyke itself*. 
On the east side of Nunthorp it gradually rises above the level 
of the neighbouring country, and might be mistaken for a gigantic 
artificial mound, had not the quarries exposed its interior struc- 
ture. A well defined ridge, about four hundred feet above the 
level of the neighbouring plains, marks its passage over the south 
flank of Rosebury Fopping. Still farther to the east it is traced 
by a gap in the outline of the moors: for the upper beds of sand- 
stone appear to have been shattered and carried off, and the 
dyke only rises to the highest level of the great bed of alum- 
shale. After passing through this gap and descending into 
Lownsdale, we found the trap forming a mass of bare rock which 
rose twenty or thirty feet above the vegetable soil. From thence 
it may be followed without difficulty many miles down the valley 
of the Esk, im a line bearing about E.S.E. Afterwards, by the 
turn of the valley at Egton Bridge, it is once more brought 
through the high moorlands; and its course is marked in that 
desolate region by a low ridge resembling an ancient Roman 
road. A quarry which is opened at Silhoue, near the seventh 
milestone on the road from Whitby to Pickering, proves the 
whole thickness of the dyke to be about forty feet, and its incli- 
nation and direction nearly the same as in the other localities. 
Beyond this place it continues to thin off, but it may be traced, 
though not without some difficulty, as far as a small rivulet about 
two miles to the east of the road. The exact point of its termi- 
nation has perhaps not been ascertained; but there does not 
seem to be any good reason for supposing that it is continued 
to the German ocean; as no vestige of it has been seen in any 
part of the cliff where it might be expected to appear. 
“ See Plate II. Fig. 3. 
