Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/21

 Coquet, near that river's junction with the sea, and bounds the coast of Northumberland as a south-south-eastern direction for 23 miles. It then crosses the mouth of the Tyne; after which the magnesian limestone begins to cover a part of it, and continues to intrude more and more upon it until both approach the Tees. The distance from South Shields to Cockfield is 32 miles in a south-westerly direction. The western side of this district cannot be so easily defined, since many of the lead-mine measures strongly resemble those of the coals field; but when the Mill-stone grits (a coarse-grained sandstone so called) and the Blue Encrinal limestone, are seen cropping out, one may then be sure that the boundary of the coal formation is passed. However, if a line be drawn from the vicinity of Aklington on the Coquet, to cross the Tyne at Bywill, the Derwent near Allansford, and the Wear below Wolsingham, and to terminate at Cockfield, a tolerably correct idea may be formed of its western limits.

This district is characterized by low round-topped hills, which rise gently from the sea, and increase in height towards the west. Pontop pike, situated on the Derwent, not far from the western boundary of the coal-field, is reckoned by Mr. Fenwick of Dipton, to be very near 1000 feet high, and a pit sunk near the summit proves that it cannot be much less. That part of Newcastle Leases which lies close to Spring Gardens, and the western turnpike gate, is ascertained to be 190 feet above the level of the Tyne, and 205 above the sea. Benwell hills to the west, and Gateshead Fell to the south, are somewhat higher.

The inequality of the surface does not affect the dip or inclination of the coal measures; and when they are interrupted or cut of by the intervention of a valley, they will be found on the sides of the opposite hills at the same levels, as if the beds had been continuous. Thus the Grindstone bed may be seen on Byker hill, Gateshead