The Macclesfield District. I. Physiography Author(S): B
Total Page：16
File Type：pdf, Size：1020Kb
The Macclesfield District. I. Physiography Author(s): B. W. Baker Source: The Geographical Journal, Vol. 46, No. 2 (Aug., 1915), pp. 117-140 Published by: geographicalj Stable URL: http://www.jstor.org/stable/1780171 Accessed: 23-06-2016 23:44 UTC Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://about.jstor.org/terms JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Wiley, The Royal Geographical Society (with the Institute of British Geographers) are collaborating with JSTOR to digitize, preserve and extend access to The Geographical Journal This content downloaded from 159.178.22.27 on Thu, 23 Jun 2016 23:44:24 UTC All use subject to http://about.jstor.org/terms THE MACCLESFIELD DISTRICT. 117 Mojsisovics, E. von. 1880. " West-bosnien und Turkisch-Croatien." In ' Grund- linien der Geologie von Bosnien-Hercegovina,' by von Mojsisovics, Tietze, and Bittner, Jahr. k. k. geol. Reichsanst., vol. 30, Pt. h\, pp. 151-266, pl. v. Penck, A. 1900. "Die Eiszeit auf der Balkanhalbinsel," Globus, vol. 78, pp. 133- 136, 159-164, 173-178. Royle, A., 1900, " Dalmatia Illustrata," viii., 80 pp., 30 pls. Sawicki, R. von. 1911. "Die eiszeitliche Vergletscherung des Orjen in Suddal- matien,11 Zeit. Gletscherk., Berlin, vol. 5, pp. 339-350, map. THE MACCLESFIELD DISTRICT. I. PHYSIOGRAPHY.* By B. W. BAKER. ? 1. Introductory. ? 2. Main Regions and Early Cycles of Erosion. ? 3. The Pre-Eocene Cycle. ? 4. The Post-Eocene Cycle. ? 5. System of Folding and Pennine Foothills. ? 6. Glacial Incident and Cheshire Plain. ? 7. Summary of Physiographical Evolution. ? 1. Introductory. The Macclesfield sheet of the 1-inch Ordnance Survey Map (No. 110) embraces an area of 12 miles by 18, Macclesfield itself lying in the north-east corner, while the other corners are marked approximately by the sites of Leek (south-east), Crewe (south-west), and Northwich. This tract of country forms part of the Midland Gate?the depression which separates the Pennines from the Welsh upland?and while it belongs mainly to the Cheshire plain, its eastward quarter consists of the foothill ranges of the Pennines. Here we have two natural regions which are readily distinguished in the contour map (see Map 2). It will be most convenient to take as a line of separation the 600-feet contour, when the relative areas to be assigned are?Pennine foothills, 18*6 per cent., Cheshire plain, 81*4 per cent. An analysis of the land-forms and physical struc? ture of the district derives most of its interest from the strong contrasts presented by these natural divisions, and it will appear later that the sharply defined boundary along which they meet has a special signi- ficance in the physical history. It will be well first to summarize the characteristics of our Hill and Plain sections. The Pennine country is one in which Carboniferous strata have been strongly folded into alternate anticline and syncline, the result being a series of steep-sided ridges oriented north and south : the summits of these are comparatively bare, with only a covering of rough grass or heather, and an occasional plantation of firs, while the valleys are deep ravines or cloughs where the picturesque streams are often buried in dense copse and oakwood. In contrast with this, one views the Cheshire lowland * Maps, p. 172. No. II.?August, 1915.1 k This content downloaded from 159.178.22.27 on Thu, 23 Jun 2016 23:44:24 UTC All use subject to http://about.jstor.org/terms 118 THE MACCLESFIELD DISTRICT. as an undulating country sloping almost imperceptibly to the west, and diversified by a greater variety of trees and hedgerows : the woods are, however, small and scattered, and Cheshire is essentially an area of park- land. The soil of the lowland consists of a thick covering of glacial clays, with sand and gravel of like origin, the solid foundation of Triassic rocks being in most parts concealed from view. The south-western part of the sheet is composed of salt-bearing strata between Alsager and Middle- wich. A reference to the hydrographical map (Fig. 1) shows that a distinc- tive system of drainage belongs to each of our natural regions. Among the hills a corrugated surface has compelled the main streams (e.g. the upper Dane, Biddulph Brook and Shell Brook) to run north or south along ready-made synclinal depressions : in isolated cases also (e.g. headstream of Trent) erosion has produced anticlinal valleys. The rivers of the plain, however, take a direction consequent on the existing slope, and their course is slightly north of west. Among these consequent streams the Dane is conspicuous. Its sinuous and trough-like valley is clearly trace- able in the contours, cutting clean across hill and plain alike. This river, along with the Wheelock which joins it near Middlewich, is ultimately tributary to the Weaver. The latter indeed receives most of the drainage of the area, only a small tract about Macclesfield and Langley belonging to the Bollin and thus feeding the Mersey. In the south-east the head- streams of the Trent rise near Biddulph; it is important to note that these south-eastern hills are the watershed dividing Trent and Weaver Basins, and so form part of the main divide for England and Wales. Here the water-parting is cut across by two remarkable depressions or gaps?at Mossley and Rushton?affording easy routes across the projecting corner of the Pennines, and giving easy communication with the Potteries and Derbyshire. ? 2. Main Regions and Early Cycles of Erosion. With these remarks by way of preamble we may proceed to a fuller analjsis of the relief. Such an analysis should be genetic in plan, utilizing the concepts of Structure, Process, and Stage, which have been rendered familiar words by W. M. Davis (see ' Geographical Essays/ pp. 249 sqq., and Geog. Jour., 14, pp. 481 sqq.), itsaim should be to show how, during a succession of physiographical cycles, an original rock-structure has been re-modelled or modified by erosive and constructive agencies until the existing surface features were evoived. Keeping this method in view, we must first state in general terms the geological facts on which the contrast of Plain and Foothills may be. said to depend. It is a commonplace of text-books that the Pennine upland is formed of the older and generally bar der Carboniferous strata, the lowland of softer Triassic deposits, mostly sandstones and marls : further, that the eflect of denudation has been to wear down the Trias to a horseshoe This content downloaded from 159.178.22.27 on Thu, 23 Jun 2016 23:44:24 UTC All use subject to http://about.jstor.org/terms THE MACCLESFIELD DISTRlCT. 119 of lowland encircling the southern Pennines, while the more resistant Car- boniferous tract remains in high relief. Such an argument attributes the Red Plain entirely to difEerential erosion, and while that explanation is k 2 This content downloaded from 159.178.22.27 on Thu, 23 Jun 2016 23:44:24 UTC All use subject to http://about.jstor.org/terms 120 THE MACCLESFIELD DISTRICT. useful as a first generalization, further inquiry will convince us that tectonie forces have been even more prominent in the chain of causation. At this point it is necessary to discuss rathei fully the stratigraphical evidence, since it is on such evidence that we must base our ideas of the topographical cycles through which the district may have passed. The whole subject is treated in a thoroughly interesting manner in Jukes Brown's * Building of the British Isles,' and the most valuable part of what follows is borrowed from that work. In the Pennines of Macclesfield the foundation is of Carboniferous strata. At the base of the series stands the limestone, a deep-sea deposit suggesting that in early Carboniferous time the site of this region was occupied by deep seas of clear water. Above the limestone lie sandstones, mudstones, and shales of the Pendleside and Millstone Grit Series ; from their composition it is argued that middle and upper Carboniferous time saw the deep seas replaced by shallower waters, the lenticular beds of Pendleside erowstone in particular pointing to the proximity of shore - lines. So we may suppose these waters to have been gradually filled in, a final stage being marked by shallow lakes and estuarine swamps in which the Coal-Measures were laid down. In this epoch one has also to postulate the existence of a northern continent running out from Scandinavia over the present site of the North Sea ; according to the observations of Dr. Sorby, it was this continent whose granites furnished the quartz and fel- spar of the Millstone Grits (Jukes Brown, op. cit., 3rd edit., pp. 162-163). But in the Coal Measure period the rivers descending southward from this land-mass must have become extremely sluggish, their basins having that low and well-graded relief which marks the old age of a physiographical cycle. In the regular geological sequence Carboniferous rocks should be followed above by Permian deposits. It will be seen, however, that the Permian is entirely absent from the Macclesfield area ; at the same time the differ? ence in these deposits on either side of the Pennines and the limitation of the Magnesian limestone to their eastern margin, prove that the seas of the period did not submerge our area.