Mr. Tate on Basaltic Rocks. 209 



both above and below it ; three different limestones come out 

 from beneath.it, and there is a coal seam among the beds, 

 now worked at Scotch Coulhard. Above the basalt are also 

 three limestones, and a coal seam three feet in thickness. 



The Basaltic Whin Sill has impressed picturesque char- 

 acters on the scenery of Northumberland ; but no where so 

 impressively as along the line of the Eoman Wall. Here it 

 attains its maximum thickness of about one hundred and 

 eighty feet — its range is more continuous for a long distance 

 — its outline is moi'e broken, and the cliffs are loftier than in 

 other parts of its course. The masses of dark grey columns 

 are much varied in form and grouping — some tower high up- 

 wards — others are broken and fragmentary — some are over- 

 hanging and threaten to fall — others are isolated and stand 

 out from the mass — and others again in the distance resemble 

 ruined towers and broken-down walls. 



These precipitous cliffs, with gaps between, are well shewn 

 near the extremity of the crags, in the Nine Nicks of Thirl- 

 wall ; from which the basalt, following the slope of the hill 

 south-west-ward, declines in height to Glenwhelt, beyond 

 which it extends westward a mile further, and then 

 bends away southward. Near the borders between North- 

 umberland and Cumberland, basalt, having a rapid dip 

 to the north, is in the bed of Burnstones burn in Kn ares- 

 dale, for about four hundred yards ; it is also in Gilder- 

 dale burn for about one hundred yards ; but it appears 

 more in Cumberland, in the streams which carry off the 

 drainage of the western side of the Pennine Chain. In 

 the North Tyne, near its head, the basalt forms a succes- 

 sion of falls sixty or seventy feet in height ; and it has 

 been sunk through at Beddy Mill, in the same district, where 

 it was found to be one hundred and twenty feet in thickness*. 

 Near the head of the Wear, a basaltic Sill appears broken by 

 the Burtreeford basaltic dyke ; and further down the same 

 river near Stanhope, there is another basaltic Sill, which Sir 

 Walter Trevelyan thinks is different from the Great Sill, and 

 situated among beds higher up in the Mountain Limestone 

 seriesf. The Whin Sill attains its maximum development 

 in Upper Teesdale, where it is above two hundred feet in 

 thickness ; and it is exposed for several miles, from above the 

 Weel near Caldron Snout to below Middleton ; its most 



* Trans. Nat. Hist, of Northd., &c, vol. ii., p. 188-189. 

 t Trans. Nat. Hist, of Northd., &c, vol. i., p. 58. 



2d 



