Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/23

 entirely absent; I have seen only a few crushed specimens of a Rhynchonella in a shale bed at Garmitage Bank. This formation occupies a considerable area in the Merse of Berwickshire; and it is well developed in the Valley of the Tweed from near the mouth of the Whitadder to Makerston, and hence the name Tuedian has been given. It appears in the Vale of Till, and on the flanks of the Cheviots. In Akeld Burn, about 100 feet of characteristic beds are tilted up against the porphyry at an angle of 85°. It is seen also in Biddlestone Burn, in the Coquet below Linn Brig, and on the Bidlees Burn. At Linn Brig, where these beds are in direct junction with the porphyry, they are highly elevated, disturbed, and shattered. A section of them is in Crawley Dene, near to Glanton; and by a great fault they have been thrown up on Garmitage Bank, 5 miles westward of Alnwick. Their relation to other formations is best seen on the Berwickshire coast, where they are intercalated conformably between the Upper Old Sandstone and the Mountain Limestone.

2. The Mountain Limestone occupies above two-fifths of the district; but it is principally spread over Northumberland northward of the Tyne. It comes out beneath the Millstone Grit in the valleys and hill sides of the South Tyne, of the East and West Allen, of the Derwent, of the Wear, and of the Tees; but, as these portions are cut off by the Stublick Dike from the northern beds, and are moreover of a somewhat different type from them, it is necessary to notice each series separately.

Northward of the Tyne the Mountain Limestone consists principally of sandstones and shales, with beds of limestone and coal interstratified, and of ironstone nodules and layers among the shales. The general direction of the strata is south-westward, with a rise towards the north-west; but in their range they are interrupted by many faults, which however have the effect of extending the same beds from the Tweed to the Tyne. They are prolonged in a narrow band along the Berwickshire coast as far as Lammerton Sheal. A line from the mouth of the Aln to the Tyne, a little east of Corbridge, nearly marks their eastern boundary. The area occupied by them in the North is narrowed