On physical grounds Sedgwick classed the Permian series with the Trias. There are instances in Lancashire, Cheshire, and Derbyshire, where a kind of gradation appears between the Coalmeasures and the Permian sandstones, which are locally conformed to them ; near Coventry the Permian beds appear conformable to the Coal-measures, and to be overlaid unconformably by the Trias; and in East Yorkshire there is considerable similarity between the beds at the base of the Permian series and those at the top of the Coal-measures, and the beds have been differently classified in places by geologists. Professor Hull, however, believes that there is an unconformability between the Permian and Carboniferous rocks in Lancashire and Yorkshire. It is considered by some observers that the different members of the Permian formation are not strictly conformable to one another. A most decided instance of unconformability is stated to occur in the railway-cutting at Tadcaster. The Middle Marl has there thinned away to a mere seam, so that the Upper Limestone rests almost directly on the Lower, and at the base of the former there is a thin bed of gravel formed of Lower Limestone pebbles.'? In isolated masses, as might be expected, it is not always easy to distinguish between the Permian and Triassic beds. Thus certain red sandstones in Lancashire, referred to the Permian period by Mr. Binney, have been considered as Bunter by Professor Hull; although the latter admits that, isolated as the beds are here, there can be no certainty regarding their age.' In some parts of Yorkshire, the Permian seems to pass upwards into the Trias. The Rev. A. Irving has remarked that there are clear signs of continuous deposition of the Permian and Lower · Explanation of Quarter Sheet 93 S.W. (Geol. Survey). Bunter rocks in Nottinghamshire ; and, so far as that area is concerned, the stratigraphical data seem to point to the conclusion that the Permian and Bunter are but portions of one great unbroken sequence of rocks. In treating of the physical history of the Permian and Triassic rocks of Great Britain, Professor Ramsay has pointed out that the beds were deposited in great inland lakes for the most part salt. One objection might be taken to this theory, inasmuch as the organic remains of the Magnesian Limestone are truly marine types. Professor Ramsay, however, observes that these are wonderfully restricted when compared with those of Carboniferous times, and in the poverty and dwarfing of the forms the fossils of this rock may be compared with the still less numerous fauna of the Caspian; so that he considers they might have lived similarly in a large inland salt lake which had previously been connected with the open ocean. PERMIAN. MAGNESIAN LIMESTONE SERIES. The name Permian was proposed by Murchison in 1841, from the ancient kingdom of Permia, in Russia. The Permian rocks consist of red sandstones, conglomerates, marls, and magnesian limestones, of which the following series is generally established : Yorkshire cor Red Sandstone and Upper Red Marl and SandUpper Permian Marl. stone. or Magnesian Magnesian Lime Upper Magnesian Limestone. Limestone Series Lower Red Marl and Sandstone. (Zechstein). stone. (Marl slate. Lower Magnesian Limestone. Lower Permian Lower Red Sandstone, Marl, Breccia, and Conglo(Roth-liegende). merate. The fossils are generally met with in the Magnesian Limestone or Marl slate; plant remains, however, are found in the Lower Red Sandstone: they include Fenestella retiformis, Productus horridus, Spirifera alata, Avicula speluncularia, Schizodus obscurus, Bakevellia, Palæoniscus, &c.; also remains of Protorosaurus and Labyrinthodont reptiles. The flora, which includes Sigillaria, Alethopteris, and Neuropteris, is nearly allied to that of the Coalmeasures; but Mr. Carruthers has observed that the Permian vegetation possesses Mesozoic affinities, and in fact that the commencement of the Mesozoic flora is to be sought in the Permian. Professor Phillips first suggested that the Magnesian Limestone should on palæontological grounds be classed as Palæozoic. The following localities where the beds are represented are given by Murchison : Red Sandstone and Marl.-West of Doncaster ; St. Bee's Head and Corby Castle, Cumberland. Hartlepool, Clacksheugh, Eldon, Thickley, Ferry Hill, Steetly (Yorkshire, Derby, and Notts.) ment of Magnesian Limestone from Brambam Moor to Nottingham. Plumpton Rocks, near Knaresborough, and Pontefract, a This statement will explain the use of some local names, such as the Pontefract rock (W. Smith), which forms a natural base to the Magnesian Limestone; the Bolsover Limestone, which is a yellowish-brown dolomite;' the Knottingley Limestone, the Weldon Wood Stone near Ferrybridge, the Fulwell Limestone near Sunderland, &c. The lower portion of the Plumpton rocks has been considered by some geologists to be Millstone Grit (see p. 90.) In Durham the thickness of the Permian rocks is about 600 feet. Lower Permian Beds.-Professor Hull has pointed out that the Lower Permian series of the western and central parts of England may be arranged under two distinct types of strata, of which those at Enville in Shropshire, and the sandstone of Collyhurst, near Manchester, may be considered as representative beds. To the Salopian type may be referred the whole of the Permian rocks as they occur in Shropshire, Staffordshire, and Warwickshire; and to the Lancashire type, the rocks of this formation as they occur at Stockport in Cheshire, in South Lancashire, and the north-west of England. The beds of the Salopian type attain a thickness of about 1,500 feet, and include: Red and purple sandstones and marls; breccia, calca reous conglomerate, sandstone and marl ; purple, red, brown and white sandstones, often calcareous. The beds of the Lancashire type include : Red marls with numerous bands of fossiliferous lime stone, worked for lime, 130 feet. These beds are con- Limestone of Yorkshire and Durham.) The evidence furnished by these types led Professor Hull to conclude that a ridge of Lower Carboniferous rocks crosses the plain of Cheshire beneath the Trias, and forms a boundary between them. Magnesian Limestone. The Magnesian Limestone is sometimes globular or botryoidal in structure ; it is usually of a yellowish colour, and sometimes contains cavities lined with crystals of calc spar. In composition it contains nearly equal proportions of the carbonates of lime and magnesia : and it is sometimes termed Dolomite or Dolomitic limestone.? The dolomitic limestone of Marsden, near Sunderland, is flexible. Some beds in Yorkshire are said to be fetid. The thickness of the Magnesian Limestone is 300 feet in Durham, and this thickness is maintained at Pontefract, the series gradually diminishing in thickness to about 120 feet near Annesley. The Magnesian Limestone has been largely quarried at Bolsover in Derbyshire, from which locality the stone used in the construction of the new Houses of Parliament was procured. There is about 12 feet of workable stone, of a pale brownish-yellow colour.3 Southwell Minster was also to some extent constructed from this stone, and partly from that at Mansfield. Quarries have been largely worked at Roach (or Roche) Abbey, near Bawtry, in Yorkshire; also in the neighbourhood of Doncaster, at Brodsworth, and Park-nook, Worksop, &c. The stone employed in the Museum of Practical Geology was obtained at Anston. At Huddlestone, the rock used in the construction of Westminster Hall was obtained. Jackdaw Craig, near Tadcaster, and Smawse ou Bramham Moor, 1 Termed Redland limestone by Wm. Smith. |
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