Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/74

 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 Wolsingham 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 line grained sandstone, used for the construction of furnaces, and varying from 5 to 6 fathoms in thickness.

4. Pattison's sill, a very hard grey sandstone with specks of mica.

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