CHAP. XXXV 
UPWARD TERMINATION OF DYKES 
1 49 
sections are taken. Mr. Barrow informs me that at Ayton a level course 
has been driven into the hill for mining operations, at a height of 400 feet 
above sea-level, and the dyke has there been ascertained to be 8 0 feet broad. 
Higher on the hill, close to the 
750 feet contour - line, its 
breadth is only 20 feet, so that 
it narrows upward as much as 
60 feet in a vertical height 
of 350 feet. Its contraction 
in width during the last 
twenty feet is still more rapid, 
and in the last few yards it 
diminishes to two or three 
feet, and has a rounded top 
over which the strata are bent 
upward. The accompanying 
section (Fig. 243) across the 
upper part of the dyke will 
make these features clear. 
Further to the west an Fk>- 24 3. — Section across the extreme upper limit of Cleveland 
.. Dyke, on the scale of 20 feet to one inch (Mr. G. Barrow), 
exposure of the upper limit 0# , Jurassio .hales, etc. ; 6, Dyke, 
of the dyke has been described 
and figured by Mr. Teall. In 1882, at one of the Cockfield quarries 
(Fig. 244), the dyke 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.” 1 
Near the other or north-western termination of this great dyke, similar 
evidence is found of an uneven upper limit. After an interrupted course 
through the Alston moors, the dyke reaches the ground that slopes eastward 
from the edge of the Cross Fell escarpment. Its highest visible outcrop is 
at a height of 1700 feet. But westwards from that point the dyke 
disappears under the Carboniferous rocks, 
and does not emerge along the front of 
the great escarpment that descends upon 
the valley of the Eden, where among 
the naked scarps of rock it would un- 
questionably be visible if it reached the 
surface. Its upper edge must rapidly 
descend somewhere behind the face of 
igneous rock 
quarry near Cockfield (after Mr. Teall). 
a a, Carboniferous shales ; b, dyke. 
F, o. 244.— Upper limit of Cleveland Dyke in the escarpment, for the 
crops out a little to the west of the 
foot of the cliff, about 1000 feet 
below the point where it is last seen on the hills above. Here the top 
°t the dyke has a vertical drop of not less than 1000 feet, in a horizontal 
1 Quart. Jour. Geol. Soc. xl. p. 210. 
