CHAP. XXXV 
UPWARD TERMINATION OF DYKES 
147 
of W. 32° H., and the same general direction is maintained by the group of 
dykes which run from the Southern Uplands across the south-west of 
Lanarkshire and north-east of Ayrshire. But proceeding northwards we 
observe the trend to turn gradually round towards the west. The dyke 
that runs from near the mouth of the Coquet across the Cheviot Hills to 
beyond Hawick has a general course of W. 8° X. In the great central 
coal-field of Scotland the average direction may be taken to be nearly east 
and west, the same dyke running sometimes to the north, and sometimes to 
the south of that line. But immediately to the north a decided tendency 
to veer round southwards makes its appearance. Thus the long dyke 
which runs from the Carse of Stirling through the Campsie Fells to the 
Clyde west of Leven, has a mean direction of W. 5° S. This continues to 
be the prevalent trend of the remarkable series of dykes which crosses the 
Old Bed Sandstone plains, though some of these revert in whole or in part 
to the more usual direction by keeping a little to the north of west. Even 
as far as Loch Tay and the head of Strathardle, the course of the dykes 
continues to be to the south of west. Tracing these lines upon a map of 
the country we perceive that they radiate from an area lying along the 
eastern part of Argyleshire and the head of the Firth of Clyde (see Map I.). 
10. TERMINATION UPWARDS 
It was pointed out many years ago by Winch that some of the dykes 
which traverse the Horthumberland coal-field do not cut the overlying 
Magnesian Limestone. The Hett dyke, south of Durham, is said to end off 
abruptly against the floor of the limestone. 1 Here and there, among the 
precipices of the Inner Hebrides, a dyke may be seen to die out before it 
reaches the top of the cliff. But in the vast majority of cases, no evidence 
remains as to how the dykes terminated upwards. I have referred to the 
Fig. 241. — Section along the line of the Cleveland Dyke at Cliff Ridge, Guisbrougli (G. Barrow). 
Scale, 12 inches to 1 mile. 
occasional interruptions of the continuity of a dyke, where, though the rock 
does not reach the surface, it must be present in the fissure underneath. 
Such interruptions show that, in some places at least, there was no rise of 
the rock even up to the level of what is now the surface of the ground, and 
that the upward limit of the dykes must have been exceedingly irregular. 
Excellent illustrations of this feature are supplied by sections on the 
line of the Cleveland dyke. Towards its south-easterly extremity, this great 
hand of igneous rock ascends from the low Triassic plain of the Tees into 
1 This is expressed in the Geological Survey Map, Sheet 93, N.E. 
