Page:Transactions of the Natural History Society of Northumberland, Durham, and Newcastle-upon-Tyne (1867).djvu/27

Rh the latter than to the former. Some thick sandstones near the bottom of the group are red, and might, if colour were a test, be mistaken for Old Red Sandstone. The Mountain Limestone, southward of the Stublick Dike, differs in some important characters from the northern series: the limestones are very much thicker and greater in the aggregate. Taking the whole series as developed in the district, and in the bordering counties, we find, from Forster's sections, a total thickness of 2080 feet, of which 470 feet are calcareous in nineteen beds, 820 feet are siliceous, and 790 feet are argillaceous. Along the Penine chain, the hills, formed chiefly of such strata, are high, massive, and rounded, with a gradual slope eastward, and a steep inclination to the west, the general dip of the beds being eastward and south-eastward. Here the name is descriptive of the formation; for the thick beds of limestone appear in great cliffs and rise to high elevations, one bed on Mickle Fell reaching a height of 2540 feet above the sea level. The whole, however, is not seen within our district; eleven only of the limestones have been observed, from the uppermost, the Fell Top, to the Tyne bottom Limestone, which, in the neighbourhood of Alston, overlies the Great Whin Sill. We have, therefore, southward of the Stublick Dike, only 900 feet of Mountain Limestone strata, of which 412 feet are argillaceous, 314 feet siliceous, 180 feet calcareous, with only about 4 feet of workable coal. The limestones come to the surface chiefly in the dales, while the siliceous and argillaceous strata occupy the higher grounds; and hence, excepting in these sheltered valleys, or where the limestone spreads over the surface, there is a wide extent of peaty moors covered with heath; and this effect is due also to the predominance of sandstones and shales in the upper part of the series, for of these there are 330 feet between the Fell Top Limestone and the Little or Second Limestone, the intervening strata being similar to those of the overlying Millstone Grit, with which it has been usual to group them.

The limestones are the most regular and characteristic strata. The Fell Top limestone, which is from 2 to 6 feet thick, appears in the dales of the Derwent, the Allen, and the Wear, coming