Mr. Forsteb's Notice of a Basaltic Dyke. 47 



stratum of Basalt continues to hold the place of the Five Quarter Seam, 

 towards the rise, is likewise unknown ; but as the workings have been 

 extended forward in that direction from the bottom of the pit, in the 

 Main Coal Seam, for about 100 yards, in which no Dyke has been met 

 with, it would certainly appear that this bed of Basalt can alone proceed 

 from the Basaltic Dyke to the dip so frequently referred to. It only 

 remains for me to add, that no appearance, which can be attributed to 

 the influence of the Basaltic Dyke, has been observed in the Main Coal 

 Seam, to the north of the shaft, although drifts have been driven from 

 the pit in that direction for about 25 yards. 



Butterknowle Colliery, near Staindrop, Feb. 13, 1830. 



Observations on the Nature and Properties of several Specimem* of Coal, 

 Basalt and Coke, from the Vicinity of the Basaltic Dyke, at Butter- 

 knowle Colliery, described in the above Notice. By Mr. Francis 

 FoRSTER, Colliery Viewer. 



No. 1. From the mixed stratum of Basalt and Coke (C), at the point 

 when it joins the Dyke. The Basalt in this specimen is of a light grey 

 colour, very fine grained and compact, and interspersed with crystals of 

 Felspar. Its specific gravity is 2-672. When submitted to a strong heat 

 in an air furnace it loses about 8 per cent, in weight, and becomes fused 

 into a brown glass. The Coke, or carbonized Coal, so intimately mixed 



with the Basalt in this specimen, is extremely hard and close grained 



fracture uneven— colour grey— mixed with irregular streaks of Carbo- 

 nate of Lime — and rather abundantly interspersed with Sulphuret of 

 Iron. Its specific gravity is 1*957 (that of the Coal which it represents 

 being 1-275). This Coke, when reduced to powder, and calcined in a 

 strong red heat, leaves 23 per cent, of a heavy incombustible powder, of 

 a reddish-brown colour. This residuum, when digested with nitric 



* These Specimens were exhibited at the Meeting, and are deposited in the Society's 

 Collection. 



