Northumberland and Durham. 27 



distance of 20 yards from the dyke ; but in others to that of 3 or 4 

 yards only. 



From the southern side of the main dyke two others branch off, 

 one to the south-east, the other to the south-west. The latter is 

 called from its breadth the 70 yard dyke, and is rilled with a body 

 of hard and soft sandstone. This intersects the upper or Beaumont 

 seam, which is not thrown out of its level by the interruption. 

 The seam however decreases in thickness from the distance of 15 

 Or 16 yards, and the coal first becomes sooty, and at length assumes 

 the appearance of coak. This phenomenon is unknown elsewhere 

 except in the vicinity of basaltic dykes. 



The south eastern branch is only 20 yards in breadth, and hard 

 white sandstone together with other rocky fragments fill the cavity, 

 and are in part cemented together by calcareous spar. Although 

 the strata are thrown up only 20 feet on the north-eastern side of 

 the vein, yet great confusion has taken place in its vicinity, and 

 much water was found to issue from it. 



From the northern side of this part of the main dyke many small 

 slips extend, some of which alter the level of the Newbiggin coal- 

 seam without affecting that of the Kenton seam lying only 13 

 fathoms above it. 



* The Birtley, Tantoby or Tanfield dyke is next in magnitude 

 and length after the main dyke. From Tatneld on the Wear it 

 ranges towards the west, passing through Leefield, Ouston, Birtley 

 Fell, and Urpeth collieries : thence in the direction of Beamish hall 

 it traverses Tanfield Moor, and crosses the Derwent near Derwent- 

 ccat Forge. In Tanfield Moor colliery it is in all an upcast on the 

 northern side of 40 fathoms ; but instead of consisting of one strong 



* I am indebted to Mr. Fenwick of Dipton for the information which follows, respect- 

 ing the other dykes which traverse the Coal-field. 



D 2 



