By chance, nor more of picturing sound
To tell the spirit of the scene.
EDMUND BLUNDEN: Dovedale
THE SCENERY of the Peak District is a treasury of features, some new, some old. Relics of the far-distant past are closely linked with others of more recent origin; some beautiful, others rugged, weird, mystifying. It is the outcome of a long process of sculpturing which was produced by slow incessant change. Throughout all these ages, however, the rocks have remained unchanged in quality and arrangement and have exerted a constant though passive influence upon the landscape. A brief consideration of the nature of that influence will provide a useful background against which to watch the development of the scenery as it exists today.
There are three main types of rocks in the district—limestone, grit and shale. Volcanic tuffs and intrusive dolerite play a minor but interesting part.
ROCKS AND SCENERY
Limestone is a hard, almost impervious stone. Consequently very little rain-water penetrates into its substance. This fact shields it from the shattering action of frost. On the other hand, it is slightly soluble in natural water. Just as a cube of sugar becomes rounded as it dissolves in tea, so the contours of the limestone surface tend to develop smooth curving outlines.
Even the purest limestone contains small quantities of dust and other earthy materials. This is left behind on the surface of the rock and accumulates to form soil. On slopes the soil is usually too shallow to give firm foothold for trees, except for the ash, but it is covered by a carpet of grass and flowers which provides valuable pasturage. The more level ground on the platforms and along valley bottoms has a covering of much deeper soil. Here trees and bushes may flourish except where the altitude is such as to expose them to the influences of strong winds.
The debris shed by the vegetation becomes mixed with the soil. There it rots and produces weak humic acids which are taken into the water percolating down through the soil and thus intensify its solvent action upon the limestone.
Limestone, like other rocks, is arranged in layers or strata, each of which is broken into more or less cubical blocks by the presence of two sets of cracks known as joints and bedding planes. Descending water finds its way down even the finest of the joints and along the closest bedding planes, and by dissolving the stone on either side widens these into open fissures. Eventually these become so spacious that most of the rain-water abandons the streams upon the surface and flows away along these newly formed underground channels. Below a certain depth all cracks and fissures are permanently filled with water. That depth is spoken of as the water-table and thus becomes the surface along which these underground streams flow.
Sometimes a surface valley is deep enough for its floor to lie along or even slightly below the water-table. In these circumstances a surface stream or river is maintained which is remarkably constant in its flow and rarely swells into flood in wet seasons or shrinks and disappears in times of drought. The Dove is a good example of this type of river.
Grit, on the other hand, is practically insoluble in water. It is, however, so porous that rain-water is quickly absorbed and, soaking inwards away from the surface, leaves this dry. The water, however, fills all the pores and cracks in the deeper layer, which then become saturated. The dry superficial parts of the grit are consequently less liable to destruction by frost action and therefore retain their angular forms and sharp edges. Some grits contain grains of felspar, a mineral which is gradually rotted by natural water. In these cases the rock disintegrates more rapidly.
Shale is more finely porous than grit. Water therefore percolates into it more slowly and is retained in its surface films. There its prolonged presence softens the rock and favours the pulverising action of frost. In areas where shale is the dominant rock, vertical erosion by streams and valley-widening proceed more rapidly. In these areas landslips occur on the steeper slopes and under the overwhelming pressure of superincumbent rocks the shaley sides of the valleys may even begin to bulge. Examples of such features may be seen around Edale and other vales.
The limestone, which is the oldest rock in this district, underlies all the others and occurs as a great mass at least 1,500 feet thick. In its uppermost portions thin layers of shale appear. Passing upwards these thicken and the intervening bands of limestone become thinner and eventually disappear. The succeeding 1,000 feet of shales are called the Edale Shales.
Thin beds of grit begin to appear in the upper levels of the shales which are referred to as the Grit Shales. Passing upwards through the rock series the grit layers become more massive. Of these there are five, of which the Kinderscout Grit may be specifically mentioned, for in the north of the district around Black Hill and Bleaklow it attains a thickness of as much as 600 feet. All these grits, however, have a lenticular form and tend to become thinner towards the south where the surface features they form are much less prominent than in the north.
Turning now to the arrangement of the rocks it will be recalled that they have all been folded, a fact which has a marked influence upon the features of the landscape. The folds are of the two general types—upfolds or anticlines and downfolds or synclines. The sides of each fold are its limbs and these link the crest of the former with the trough of the latter. The rock layers are horizontal or nearly so at these two points but are more or less steeply dipping in the limbs.
Erosive or denuding agencies naturally attack the upfolds to begin with and in doing so strip away the younger rocks first and the older ones in turn until in the centre of the crest the limestone is brought to view as in the Derbyshire upland. Northwards from the upland, earlier stages in this stripping process are exemplified in succession. In the moorland area much of the grit cover still remains. On the other hand, on the downfolds the youngest rocks survive longest in the centre of the trough, hence the presence of Coal Measures in the lower Goyt valley. Along the zones of country occupied by the outcropping limbs of the folds the rocks dip down from the surface and the edges of the strata produce such scarp-like features called “edges,” as Axe Edge, Froggatt Edge, Baslow Edge and Black Edge (Fig. 4, see here).
TIME AND SCENERY
The Peak District is but a minute portion of the earth’s crust. This latter is often spoken of as “terra firma” as though it were quite rigid. But it is rigid only in the sense that a block of wood is rigid. Anyone who has jumped off a diving-board knows, however, that when the block is so long that it becomes a plank it is springy and flexible. The rock layers which make up the Peak District are similarly flexible. Deep down in the earth beneath them lies a plastic foundation which during long periods of time has crept slowly from one region to another and the crust of rocks which rests upon it has risen and fallen accordingly. In the middle and again in late Pliocene times movements of this kind took place in the Peak District and resulted in a general uplift of the region. Each uplift probably took place in a series of stages but, for the sake of brevity with clarity, only the total results will be considered for the two occasions.
With each total uplift of the Peak District its level above the sea was increased. Consequently all the agencies which had almost gone to sleep were aroused into activity once more; water flowed more rapidly; vertical and later on horizontal erosion were renewed. Thus it came about during the remaining 15 million years of Pliocene, Pleistocene and recent times, that rain and rivers, frost and glaciers gave to the district those magical touches of beauty which make it so attractive to its many visitors.
The process of carving the surface was by no means haphazard. On the contrary, as the result of successive uplifts there was a majestic rhythm about its progress which inscribed its score everywhere. For those who learn to read that score the appreciation and enjoyment of the scenery are greatly enhanced. How was that score written? That is the next problem to be explored.
The key agents in carving inland scenery have always been the rivers and streams. Those of the Peak District are all tributaries of large rivers—the Mersey, Trent and Don—which in turn pour their waters into the sea. This last phrase, though trite, leads straight to the central influence that ultimately controls the whole activity of running