in Yorkshire and Durham. 41 
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. Wharton 
ascertained its continuity, by examining the thickness, the dip, 
and the bearing, of several masses of trap, which appeared 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 Teesdale, should be correctly 
determined, is certainly an object of considerable interest. 
The following facts appear of most importance in illustrating 
the natural history of this dyke. 
(1) The trap, in colour, fracture, and external form, is similar 
to that of Cockfield Fell. It often parts into irregular prismatic 
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 progress 
westward. Thus, at Crowtrees quarry it is six feet and a half 
wide—at Tarsdale quarry nine feet and a half—at Bitchburn 
bank fifteen feet—and still farther 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. 
Crowtrees, 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. Wl. Part I. F 
