Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/268

 Permian beds referable to the Salopian type to the north of this part of England, except in the case of the little outlier at Rushton Spencer, north of Leek, where they occupy a small area, and rest directly on Lower Carboniferous beds of the Yoredale series. Their occurrence at this spot was first pointed out by Mr. E. W. Binney*, and more recently by Mr. A. H. Green in the memoirs of the Geological Survey†. Both of these geologists concur in considering the beds to be of Permian age ; and their position with reference to the Lower Carboniferous strata on which they rest is a point of interest and importance as bearing on the question concerning the extent of the denudation of the Carboniferous rocks before the Permian period in this locality, coincident, as it is, with the axis of elevation, to which I shall again refer, and which forms the special subject of our inquiry.

Mineral Characters of the Salopian Type of Permian Beds. — It may, I think, be safely affirmed that over the whole tract of country above described the Permian beds belong to the Roth-todt-liegendes or lower stage, and are all of one type — and this notwithstanding local and exceptional interpositions of peculiar beds deriving their origin from the agency of ice (as shown by Professor Ramsay in the case of the trappoid breccias), or on account of marginal conditions, as shown by Sir R. Murchison in the case of the Cardeston brecciated rock. With these and similar exceptions, the whole series (attaining a thickness of 1500 or 2000 feet in Warwickshire) consists of an assemblage of brown, red, or purple sandstones, often calcareous, alternating with red shales and marls, and characterized by much irregularity in the stratification. Both the sandstones and the local breccias and conglomerates are distinguishable from those of the Bunter Sandstone with which they usually come in contact ; and the frequent interposition of beds of red marl gives the group a fades differing from that of any of the divisions of the Bunter Sandstone. Such is the character of these beds, whether we find them in Denbighshire or Shropshire on the one side, or in Warwickshire on the other. They form a group of strata of themselves, differing in their mineral characters from the Permian rocks either of the North- west or North-east of England. Their original marginal limits may at intervals be traced both in Shropshire on the west, and in Leicestershire and North Staffordshire on the east, notwithstanding the obscurity occasioned by the overspreading of the Triassic formation. The beds at Rushton Spencer form, in my opinion, a marginal outlier, deposited in a hollow, along the line of the barrier of Lower Carboniferous rocks, which originally divided the beds belonging to the Salopian type from those of the Lancashire type.


 * Memoirs of the Lit. and Phil. Society of Manchester, vol. xii.

† "Geology of Stockport, Macclesfield, &c.," by E. Hull and A. H. Green. The position of these beds is shown in a section by Mr. Green in our joint paper " On the Millstone Grit of north Staffordshire &c.," Quart. Journ. Geol. Soc. vol. xx. p. 260, fig. 7.