64 Mr. N. J. Winch on the Geology of 



substance imbedded in them. This is one of the uppermost strata 

 on the Derwent, where it crops out, and is quarried for millstones. 

 The quarries are on Muggleswick Fell, and also between Wol- 

 singham and Stanhope in Weardale. The thickness of the rock at 

 Muggleswick is about 5 fathoms. The hilly district of the lead 

 mine country affords but one stratum of this rock, which crops out 

 before it reaches Aldstone moor or Allendale. It is probably the 

 same bed which is found in the section of Arkendale. A similar 

 rock is found in the north-eastern part of Northumberland at 

 Scramerstone four miles south of Berwick, and at Craster near 

 Howick; and with this durable material the castle of Dunstanborough 

 is built. The grey millstones of Muggleswick are employed for 

 grinding rye, but those brought from Derbyshire are preferable in 

 quality. 



5. The grindstone sill, a fine grained yellowish sandstone, which 

 on Aldstone moor, Coal cleugh, and Allenheads is the uppermost 

 bed, and is found near the surface at Nent head and on the summit 

 of Cross Fell. On Aldstone moor its thickness is about 4 fathoms. 

 Grindstones, greatly inferior to those of Newcastle, are made of it 

 for home consumption. 



Below the limestone in the Aldstone moor section the following 

 other sandstones may deserve notice. 



1. The whetstone sill, a fine grained micaceous sandstone, which 

 may be seen at this day at Burtreeford. 



2. The iron-stone sill, a ferruginous sandstone, containing iron 

 pyrites in abundance. 



3. Firestone, a porous fine grained sandstone, used for the con- 

 struction of furnaces, and varying from 5 to 6 fathoms in thickness. 



4. Pattisons sill, a very hard grey sandstone with specks of mica. 



5. The coal sills, many of them resembling the last. 



