RE-EMERGENCE
The Mesozoic Era lasted about 120 million years, during which the Peak District lay hidden under an ever-increasing cover of limestones, sandstones, clays and chalk. The time of its eclipse was now, however, drawing to a close, for the British area, after its prolonged period of sinking, began to rise once more. The floor of the chalk sea was uplifted and converted into dry land, an event which marked the opening of the Cainozoic Era.
This uprising did not take place uniformly over the whole area but was most marked along a line running northwards through the area of the Peak District and the Pennines and resulted in the appearance of a low elongated dome. This formed an island which had the scenic features of chalk downs. The crest of this dome served as a natural water divide and many streams flowed down its gentle slopes. The sea floor continued to rise and the boundaries of the land were extended outwards in all directions. The streams lengthened out across the broadening plains as these rose out of the water. Uniting with one another they merged into larger rivers flowing to the sea which by this time was far away.
Wherever streams and rivers flowed they excavated channels which as they deepened were widened into valleys. All this involved the gradual removal of large quantities of rock. The chalk was the first to be attacked. After that the more deeply seated layers of the Jurassic and Triassic rocks were penetrated, a piece of work which was begun and carried farthest upon the original dome. There at last the Carboniferous rocks began to peep out along the beds of the streams. The latter continued to carry away the waste formed by the gradual destruction of the younger rocks on either side of the valleys. But still the streams went on cutting their channels more and more deeply into the Carboniferous rocks. These channels were also widened into valleys and these old rocks came to occupy a correspondingly larger portion of the valley sides. The Mesozoic rocks were steadily reduced to mere remnants capping the hills on either side. Eventually even these disappeared completely and left the Carboniferous rocks in sole possession of the Peak District.
The long eclipse had ended. The precise date for that event is unknown for the complete removal of all the waste from the destruction of so much rock left no tangible evidence behind. It is, however, probable that it happened shortly before or at the opening of the Pliocene period, which was the last of the four major periods into which the last or Cainozoic Era has been divided.
The removal of the Mesozoic rocks was not the only great event that happened during this long period of time. The living garment that clothed the landscape also changed. True flowering plants that produced seeds in closed caskets had come into being in other parts of the world during Cretaceous times. These invaded the new lands as they rose into being over the British area. Among them were many kinds of woodland trees and numerous flowering herbs and grasses which covered the ground as with a multi-coloured carpet. Over this beetles crawled, butterflies flitted and bees hummed. Winged reptiles had passed into oblivion and their place was taken by birds. The long reign of reptiles was over and only a few insignificant representatives remained. On the other hand, mammals were rising rapidly to a position of dominance. A wonderful variety of insect-eaters, vegetable and flesh feeders haunted the woodlands and sported on the grassy plains. Many of these began to show recognisable resemblances to modern and familiar types, to horses, deer, wolves, cats and monkeys. Usually they showed some features that would seem to us to be peculiar.
The Peak District now entered upon the last phase of its long and eventful history. The carving of the scenery as seen now had begun. Even during the time of its eclipse the blue-print for the general arrangement of its hills, valleys and moorlands was being drawn. When in early Cainozoic times the streams and rivers first began to score the surface of the chalky slopes, their direction of the flow was the same as that in which the Mesozoic rocks were dipping. Just as a saw when it has begun cutting through a log of wood must keep to the same line in which it started, so likewise a stream, having once made a track, must keep to it. Having made its bed it must lie on it.
Thus it came to pass that the arrangement of streams laid down upon the surface of the chalk was eventually incised into the underlying Carboniferous rocks. These, however, had been folded long ago and the layers had been tilted at varying angles in differing directions. Henceforth the streams flowed on regardless of the directions in which the rocks dipped or of the way in which they were folded. Such a drainage system is said to be superimposed. One outcome of this is that the scenery along the valleys is more varied than alongside normal streams. Thus, for example, in the main valley of the area, that of the Derwent, grit scars, limestone gorges and wide fertile dales alternate with one another.
THE ICE AGE
One last event remains to be mentioned. The period popularly known as the Great Ice Age was on the whole a time of mild and even warm climate, interrupted now and then by polar conditions when icefields formed over the mountainous regions and, flowing thence, covered the lowlands and filled up the adjoining sea basins. During one of the earliest of these interruptions, or glaciations, all but the extreme south of England was covered with ice. Nevertheless the presence on the South Pennine moorlands of rocking stones and other stones fantastically shaped by prolonged weathering in pre-glacial times indicates that some of the highest parts of the Peak District were never subjected to the scouring action of overflowing ice.
During a later glaciation ice from the Irish Sea invaded the lowlands of Lancashire and Cheshire and, impinging against the flanks of the West Moors, attained an altitude of 1,250 feet. At that time a trickle of ice finding its way across a gap at the Dove Holes, northwest of Buxton, entered the tributary valleys of the Derwent and even reached the vicinity of Matlock. This ice did not, however, leave any appreciable impression upon the scenery of the district. Nevertheless, whenever such arctic conditions prevailed they intensified the action of more normal agents. The snow which accumulated in the winter melted in the early summer. On the shale areas the ground became sodden in the daytime and frozen at night with the result that soil creeping and land sliding took place on a massive scale and greatly accentuated the concavities of the valley slopes.
Elsewhere in England and north-west Europe, Old Stone Age Man appeared upon the scene and gained a livelihood by hunting. Outside the Peak District, though quite near, the caves at Creswell have yielded a very full and unique record of his sojourn in this part of England. In striking contrast is the solitary discovery of one flint implement referable to that time within The Peak in the vicinity of Wirksworth. It is sufficient, however, to indicate that Palaeolithic Man was an occasional visitor. As will be seen later, evidence for the presence of prehistoric man is much more abundant in post-glacial times.
REFERENCES
MARSHALL, C. E. Guide to the Geology of the East Midlands. University of Nottingham (1948)
Memoirs of the Geological Survey
WRAY, D. A., EDWARDS, W., and TROTTER, F. M. The Pennines and Adjacent Areas. Third edition. British Regional Geology. H.M.S.O. (1954)
WATERS, R. S. and JOHNSON, R. H. The Terraces of the Derbyshire Derwent. East Midland Geographer: 9 (June, 1958)
Approach we then this classic ground: