44 Mr. Fobsteb's Notice of a Basaltic Dylee. 



No. VIII. — Notice on the Effects of a Basaltic Dyke, at Butterknowle 

 Colliery, two Miles North West of Cockfield. By Mr. Michael 

 FoRSTER, Colliery Viewer. 



Read March 16, 1830. 



"^Ihe Basaltic Dyke, to which the following observations refer, is well 

 known by the name of the " Cockfield Dyke," the thickness of which 

 is from 18 to 20 yards, and its line of bearing nearly from east to west. 

 By the intersection of other Dykes of considerable magnitude, near the 

 point where the accompanying sections have been taken, the thickness 

 of this great Basaltic Dyke is greatly diminished, and its line of bearing 

 altered several degrees to the south of west. The observations, how- 

 ever, which I have the honour of laying before the Society at present, 

 will be confined to the effects produced by this Dyke on the two seams 

 of Coal which have been opened out under my superintendence, by the 

 sinking of a pit called the William pit, at Butterknowle Colliery, the 

 property of the Rev. W. L. Prattman, and situated about two miles to 

 the north west of Cockfield. 



I cannot better explain these appearances and effects than by relating 

 them in the order in which our various operations brought us in contact 

 with them. In driving forward the discovery drift A B {see Plate IX.) 

 from the dip to the rise in the lower or Main Coal Seam, it was found that, 

 within 1 1 yards of the Basaltic Dyke, the seam of Coal was displaced by 

 a layer of Basalt and charred Coal, intimately mixed together, and having 

 the same thickness and inclination as the seam itself. Of the appearance 

 presented by this mixture a tolerably accurate idea may be formed by re- 

 ferring to the accompanying section, at C, where the Basaltic matter is 

 coloured red, and the Coke, or charred Coal, dotted black. The charred 

 Coal thus intermixed with the Basalt was so compact and hard (arising, 



\ 



