This wall breaks through the oolite and lias rocks at Mayhecks, 

 crosses the Murk Esk near Grosmont, is also seen at Ainthoipe, 

 Oastleton, Commondale Kildale, Easby moor, Ryehill, Ayton, 

 Is'unthorpe, cutting through the rhoetics near Newby, and pierces the 

 New red sandstone at Stainton, Preston, and at Coatham beck, near 

 the village of Elton. Following it into Durham we find it no where 

 in contact with the magnesian limestone. In the carboniferous 

 rocks at Bolam, it is again found, but has deviated from the wall 

 formation, and by lateral intrusion has formed a small whin sill, it 

 may be traced through the carboniferous rocks to Cockfield fell and 

 onwards. Mr. Teall followed it up to Woodland ft-ll, a point one 

 mile east of Middleton. Mr. Howell, superintendent of the geolo- 

 gical survey in Scotland, points out other exposures, one 1^ miles 

 N. E. of High Force where the dyke crosses Bowles beck, another 

 about one mile south of Tyne head. It is traced in the Eden 

 valley, having passed through the Penine range and entered again 

 into secondary rocks where it becomes the Armathwaite dyke. 



This intrusive rock is fairly straight in its course with occasional 

 slight deviations ; it varies in thickness from 20 to 80 feet. Here 

 at Ayton, it is 80 feet thick at the base of Roseberry, whilst at the 

 highest part of the intrusion it is only 20 feet. In some places in 

 its course it appears to die out, not having penetrated through the 

 superincumbent stratification. 



To use Mr. Barrow's words ' ' another interesting point is the 

 unevenness of its upper surface, as it frequently disappears for a 

 considerable distance, and then reappears. When first seen, in the 

 western area it occurs in soft shales, and, in consequence, forms a 

 strongly marked ridge, as is well seen about Langbaurgh and Cliff 

 ridge. As far as the top of Cliff ridge the dyke reaches the surface, 

 but does not appear on the east slope of the hill. The drift makes 

 it doubtful whereabouts it again crops out, but there is a large 

 quarry in it at Slack's wood. Just beyond this it must again sink 

 beneath the surface, reappearing only at one point in Howl road. 

 The calcined ironstone and several trial holes show that it has just 

 failed to burst through the solid rock here." 



This feature of the dyke is described as occurring in other parts 

 of its course by the same observer. Mr. Teall also describes the 

 same effect occurring in the coal measures at Cockfield, Avhere "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." 



The effect upon rocks in contact has been comparatively slight ; 

 heat has calcined them for a few feet distant, and coal is completely 



