in Yorkshire and Durham. 257 
near Durham, communicating some very interesting facts con- 
nected with the appearance of a basaltic dyke; which ranges 
from the escarpment of the magnesian limestone (at Quarring- 
ton Hill, a few miles to the east of Durham) through the great 
coal-field, in a direction about W.S.W. _ It is found along this 
line at Crowtrees, Tarsdale, Hett, Tudhoe, Whitworth, and 
Constantine farm. From the last-mentioned place, it passes 
along the same line of bearing, through the collieries of Bitch- 
burn and Hargill Hill, to a spot near the confluence of Bed- 
burn Beck and the river Wear, where it is well exposed on 
the surface of the ground; and it is known to pass up the Bed- 
burn Beck valley towards Egglestone Moor. If prolonged 
a few. miles in the same direction, it must meet the line of the 
Cockfield Fell dyke within a short distance of Egglestone ; 
and may, perhaps, be a prolongation of one of the masses of 
trap described in a former part of this paper. 
This dyke is laid down in none of our geological maps. 
Indeed its existence was probably unknown before Mr. Whar- 
ton ascertained its continuity, by examining the thickness, the 
dip, and the bearing, of several masses of trap, which ap- 
peared in separate quarries, but in the same general line of 
direction. That its further extension towards Egglestone 
Moor, and its probable connexion with the trap of High Tees- 
dale, should be correctly determined, is certainly an object of 
considerable interest. 
The following facts appear of most importance in illustra- 
ting the natural history of this dyke. 
1. The trap, in colour, fracture, and external form, is simi- 
lar to that of Cockfield Fell. It often parts into irregular pris- 
matic blocks with well defined angles, and four or five plane 
sides covered with an ochreous crust. 
2. The width of the dyke appears to increase in its pro- 
gress westward. Thus, at Crowtrees quarry it is six feet and 
a half wide,—at Tarsdale quarry nine feet and a half,—atBitch- 
burn bank fifteen feet,—and still further west it is seventeen 
feet wide. 
3. It dips to the north. at an angle which brings it up in 
a direction which is nearly perpendicular to the coal strata; 
which, on the north side of the dyke, are. found about twenty- 
four feet above the level of the corresponding beds on the 
south side. 
4 In the collieries situate in its line of direction (viz. Crow- 
trees, Bitchburn, and Hargill Hill) the seams of coal near the 
dyke are charred, or converted into a hard mass of cinders; 
in consequence of which, the works have in some cases been 
partially abandoned. 
Vol. 67. No. 336, April 1826. 2K 5. The 
