Northumberland and Durham. 93 



This rock is very much like a fine-grained sandstone, and contains 

 so large a portion of silex and clay as to be scarcely worth burning 

 for manure. It would be called a bastard limestone. This bed 

 appears to be one of the lowest in the series to which the metal- 

 liferous limestones belong ; it occurs in the north-western part of 

 the district, and is not uncommon in Roxburghshire, lying very 

 near the red sandstone. 



Porphyritic Formations of the Cheviot Hills. 



A considerable tract of the north-west of Northumberland is oc- 

 cupied by the Cheviot hills, which rising from below the stratified 

 country of the Lead-mine measures, stretch westward into Roxburgh- 

 shire. The higher parts of these mountains being covered with 

 peat moss, and their lower acclivities with alluvial soil, it is not easy 

 to trace the exact line of separation between the porphyritic rocks, 

 of which they consist, and the Lead-mine measures. It has been 

 seen however that to the north the porphyritic rocks do not descend 

 to the banks of the Tweed ; to the south-west, limestone is quarried 

 on the sides of Carter Fell, and a small colliery is worked at 

 Kedderburn in the same neighbourhood. Towards the south, por- 

 phyry is seen on the banks of the Coquet at Linn-bridge, a mile and 

 a half south of which, on the hill at Woolcoats, several coal pits are 

 worked. For the other boundaries of this range I must refer to the 

 map. 



Cheviot, which gives its name to the whole group, is a huge 

 round topped mountain, rising 2642*. feet above the level of the 



- * Leslie's Elements of Geometry, 2d edit. 



