Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/269

 I now pass on to trace the characters and distribution of the Permian rocks of the latter type.

Permian Beds of the Lancashire Type.

Distribution. — A fine exhibition of these beds may be observed along the banks of the Mersey, above Stockport, where they are interposed between the conglomerates of the Bunter Sandstone and the coal-measures of Cheshire. Passing towards the north and west, we find them opened out on a large scale at Collyhurst, near Manchester, where they were first identified as of Permian age by Mr. Binney*, as being clearly overlain by a series of marls with limestones containing fossils of Permian genera. Prom Manchester, they have been traced by the same geologist, along the southern margin of the Lancashire coal-field to Whiston, near St. Helens; and throughout they occupy a position of discordance, both as regards the Trias above and the coal-measures beneath. At Stockport the formation attains a thickness which I have estimated at 1500 feet. Whether or not it is so great, it is undoubtedly considerable ; and had it not been for the superposition of the fossiliferous marls and limestones, which have been clearly determined to overlie this rock, by borings at Heaton Mersey, the whole (as far as lithological character is concerned) might have been regarded as of the Bunter Sandstone age.

Mineral Characters and Composition. — Instead of a series of interstratified sandstones, marls, breccias and conglomerates, such as that which forms the Lower Permian rocks of the Salopian type, we have in Cheshire and Lancashire a mass of homogeneous sandstone, resembling in every respect (except in position) the lowest division of the Bunter Sandstone of Shropshire and west Cheshire. This rock is generally so soft as to be used for foundry purposes, and consists of bright red and variegated sandstone, without pebbles, fine-grained, and traversed by planes of current- lamination.

When I first saw this rock in the quarry at Collyhurst, and judging only by mineral character, I thought I recognized in it the " Lower Mottled Sandstone " of the Bunter, with which I had been so familiar in Shropshire and west Cheshire ; but the position of the fossiliferous marls which here overlie this sandstone, and which contain remains of the genera Turho, Rissoa, Natica, Gervillia, Axinus, Myoconcha, and Tragos, determines beyond doubt the Permian age of the sandstone rock, as shown by Mr. Binney. It clearly forms a lower stage of the Permian formation in this part of England.

The contrast between these beds and their representatives in Shropshire and the midland counties is, in fact, as great as between the Bunter Sandstone and Permian beds of those counties. The Upper Permian series of South Lancashire requires but short


 * " On the Geology of Manchester," Trans. Geol. Soc. Manchester, vol. i.