Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/276

 somewhat as shown in the accompanying section (fig. 2 ; see also map, page 183). The Coal-measures on each side of the supposed Axis. — As there is no evidence of any similar axis, we may suppose that the coal-field extends from the northern flank of the Cheshire axis to the borders of the Lancashire Coal-field on the north, which, with that of Flintshire on the west and Poynton on the east, must form one continuous sheet (see map). To the south of the axis the coal-measures may also be supposed to stretch for a considerable distance, and to be continuous with those of Denbighshire and North Staffordshire. The southern limits of this coal-tract are in all probability very irregular and indented, owing to the proximity of the ancient margin of the Carboniferous area. Should the plains of Mid-Cheshire ever be pierced in search of coal, which from the enormous thickness of the overlying secondary rocks appears hopeless, care will be required to avoid striking upon the rocks below the coal, in the line of the anticlinal axis and along the southern margin, indicated by the lighter shading on the map.

The Permian Beds on each side of the supposed Axis. — The existence of such an axis of elevation as is here indicated, formed at the close of the Carboniferous period, and belonging to the "Pendle system " of flexures, serves, I think, to explain the difference in the character of the Permian formation to the north and to the south of such a line in a more satisfactory manner than any other hypothesis. The elevation of the Lower Carboniferous rocks into ridges, from which the coal-measures were swept away partly by atmospheric, partly by marine, denudation, would produce a ridge, or ridges, of land-surface dividing the Permian basin on the north from that on the south. That the Carboniferous rocks were thrown into such ridges flanking the Permian sea, is clear from the position of the beds at the northern base of the Pendle range at Clitheroe. To admit of this hypothesis, we are not required to adopt a speculation which has no example in this part of the country ; while it helps to solve the problem why the Permian beds on either side of this ridge belong to two distinct types, the Salopian and the Lancastrian.

Conclusion.

In conclusion, I regard the axis under the Cheshire plain as merely the prolongation of the Carboniferous barrier which separated the Permian basin of the north of England from that of the Midland counties and Shropshire. The barrier was apparently prolonged towards the district of Charnwood Forest, where it was composed of Cambrian rocks, and was formed for the most part of Mountain Limestone, Yoredale beds, and Millstone Grit, on either side of the barrier. The Permian formation itself gives evidence of the proximity of land ; for on the north side the Magnesian Limestone becomes deteriorated both in composition and thickness towards Nottingham, and on the other the Permian beds along the skirts of the Leicestershire Coal-field are evidently marginal representatives