The fauna in the waters underwent a corresponding change. The stone lilies, corals and many of the brachiopods and molluscs departed from the area. A few of the last remained and were joined by other kinds of goniatites and bivalves. Meanwhile the deltas and sandbanks extended and began to invade the district from time to time. The quality of the water also changed from being saline through brackish to fresh. Marine animals disappeared and were succeeded by a less varied and sparse population. At first this included Lingula, a curious tongue-shaped brachiopod which had already existed for 250 millions of years from Cambrian times onwards, and was destined to continue in the world for a similar stretch of time until the present day. As the waters freshened still more, Lingula and its associates migrated elsewhere and were replaced by crowds of bivalves such as Carbonicola which resembled the mussel of the present-day rivers and canals. Towards the close of this phase in the story of the Peak District the occasional influxes of coarse sediments became more copious. Banks of grit and gravel were formed and ultimately became that massive hard rock known as Millstone Grit.
Owing to slight oscillatory movements in the level of the region these deposits were sometimes raised above water level and produced a low-lying landscape of sandbank and water channels. Spores wafted by the breezes, seeds carried by the streams from the continent enabled plants of the northern continent to settle on this new land surface. In the warm moist atmosphere they quickly germinated and produced a jungle growth of fern-like plants and strange-looking trees. Of the latter the smaller ones resembled the Tree Ferns which now grow in the tropical forests of the East Indies. Others, known as Calamites, were closely related to the horse-tails, those tall weeds which look like miniature Christmas trees and today grow profusely in wet waste places. Some of the trees towered to a height of 60 or 80 feet and had trunks as much as five feet thick. The bark was often decorated with scale-like markings which suggested the name Lepidodendron (lepido=scale) for these trees. Their branches and twigs had a furry covering of small lancet-shaped leaves. The modern relatives of these trees are not to be sought for in luxuriant forests but on bleak moorlands where the Stags Horn Moss (Lycopodium) is to be found straggling through the grass. These plants do not grow from seeds but, like ferns, they reproduce by means of minute pollen-like spores.
Among the undergrowth of ferns and in the pools and sluggish streams were lowly types of four-legged animals, represented today by newts or salamanders, creatures which resemble fishes in that they lay their eggs in water and their young must spend at least the early part of life breathing by means of gills.
These conditions, so different from the present, lasted long enough for deep deposits of vegetable debris to accumulate and become peat. A gentle down-sinking of the whole region then ensued. The sandbanks with their cloak of peat were submerged and were gradually buried under thick beds of mud and clay. The peat, squeezed by the pressure of the increasing load and changed by complex chemical reactions ultimately turned into coal. The mud also was compacted into shale.
The sequence of events last portrayed was repeated a number of times and thus was built up a series of massive grit layers interspersed with shales and occasional seams of coal. These rocks were all destined, in the fullness of time, to play a large part in the scenery and other amenities of the Peak District. The layers of grit and shale, which had attained a thickness of a thousand feet, extended far beyond the bounds of the district and covered a vast area including the north of England and southern Scotland.
The transport of so much sediment from the North Atlantic continent implies a corresponding destruction of the rocks in its uplands and a general wearing down of its whole surface to lower levels. As one outcome of all this the formation of coarse grit ceased and henceforth only fine sand, silt and mud were transported into the southern waters. Deposition and sinking went on in unison continuously, except for an occasional upward oscillation which converted much of the region, including our district, into an extensive fenland of mud-flats, upon which forests grew once more and thick peats accumulated. When the sinking movement was renewed, sea-water sometimes flowed in and spread everywhere, bringing with it marine animals, especially goniatites. Such marine conditions lasted only for a short time and gave place to a long period of fresh-water conditions when mud accumulated and buried the peat, which was in turn converted into coal.
In this way 4,000 feet of clays, shales and fine sandstone with occasional coal-seams and marine bands accumulated. These are spoken of collectively as the Coal Measures. The economic importance of the coal suggested the word Carboniferous as the most suitable name for the whole sequence of rocks hitherto dealt with, including Mountain Limestone, Edale Shales, Millstone Grits and Coal Measures; and for the long period of time, amounting to 60 millions of years, which they represent.
The countryside now occupied by these Coal Measures is comparatively low-lying. Apart from tip heaps it has a scenic beauty of its own but makes no contribution to the amenities of the Peak District. It does however provide the basis for the livelihood of dense populations. From its cities at week-ends and holiday times streams of hikers and pleasure-seekers pour forth to find renewal of energy and refreshment of mind and spirit in the dales and on the moors.
THE ARRANGEMENT OF THE ROCKS
The process of forming those rocks which make up the Peak District was completed millions of years ago. Two sets of agencies then came into action and recorded their activities in quite different characters. One, which was concerned with rearranging the rocks, completed its work in a relatively short period of time. The other, concerned with destroying and carving the rock of the district, experienced a long interruption of its activities during the Mesozoic Era.
The hiker on Kinderscout or Bleaklow rejoices in the fresh breezes and in the fact that he is 2,000 feet or more above the sea. Though he takes that fact for granted it is nevertheless full of significance. Kinderscout is a little plateau with a relatively flat surface defined along its margins by rough, often precipitous slopes of Millstone Grit, for that is the rock which immediately underlies the plateau. When it was formed, that slab of grit was part of an extensive sandbank lying close to sea-level. As already seen, it was subsequently buried under Coal Measures down to a depth of some 5,000 feet, that is to say 7,000 feet below its present level. How then did it come to be at its present height? This was brought about by the joint action of two types of movement of the earth’s crust, of which the first must now be discussed.
Just as the process of burial described above was being completed, great revolutionary events began to take place across the south of the British area and the north of France. Mighty pressures in the earth’s crust acting from north and south crumpled the rocks along a belt of country about 200 miles wide and heaved them up into a mountain range of Alpine and even of Himalayan proportions. A small backwash of these great events was felt in the region of the Peak District. That threw the Carboniferous rocks into a number of folds which have exerted an important influence upon the physical features as seen today. As one result, the western margin of the district was crumpled into a series of narrow folds which merged into the main axis of the Pennines. Chief among these was a broad fold, elongated from south to north, which is known as the Derbyshire Dome. In cross-section it is asymmetrical and has the form of a wave that is just about to break; that is to say its eastern side or limb rises slowly to a crest from which the western limb drops down more rapidly and is broken by a series of rock fractures or lines of faulting. The slowly rising eastern limb is itself crossed by a succession of minor folds which run at right angles to the crest and which curve southwards beyond the east margin of the dome.
It is, of course, impossible to see a complete section across this and the other folds at any one point, but the visitor wandering from