A HISTORY OF DERBYSHIRE shales. The north side is formed of a dip slope of a bed of sandstone which crops out from under the shales. The river runs along the top of the lower sandstone with a steep cliff of shale on the south, which it is undermining and wearing backwards. A third class of valley has been caused by streams flowing down the escarpment of one of the parallel valleys and cutting back into the hill until at length a transverse valley is formed. The oldest rocks in the county are found in the hilly districts. Their position with regard to the newer rocks by which they are surrounded and the folds into which they have been bent afford evidence of the Pennine upheaval and the subsequent denudation which the rocks have undergone. The sedimentary rocks which were deposited in horizontal beds have, subsequently to their formation, been bent into numerous folds by lateral pressure. Consequently a bed may be hori- zontal in one place and inclined to the horizon in another. The amount of inclination or dip may also vary from place to place. A horizontal section through the country would show a series of arches or anticlines, in which the strata dip away from a point to the east and west, and of troughs or synclines, in which the strata dip towards a point from the west and east. A comparison of several sections parallel to one another shows that the anticlines and synclines are bent over lines or axes, which are called anticlinal and synclinal axes. Where the rocks have been also folded by a second pressure almost at right angles to the first they form domes and basins. In the former they dip away in all directions from a central point or line, in the latter they dip from all sides to a central point or line. A well marked anticline passes through the district in a north- westerly direction. The beds dip steeply to the west under the Coal Measures of Lancashire and Staffordshire, and with a more gentle dip to the east, under those of Yorkshire and Derbyshire. The Coal Measures of East Derbyshire in their turn dip under the Permian or Magnesian Limestone series. In the northern part of the county a dome-shaped mass of mountain limestone has been brought up. The severed strata on the west and east sides of the anticline which were once continuous across the arch have been removed by denudation which has not only laid bare the mountain limestone, which is the lowest rock reached in Derbyshire, but also removed a small thickness of the uppermost beds of limestone. If we were to start on the mountain limestone and travel a short distance in a westerly or easterly direction we should pass over the various members of the Carboniferous series of rocks in succession up to the Coal Measures, and on the eastern side of the county should arrive at the Permian limestone. A smaller anticline parallel to that of the Pennine Chain passes through Ashover. At Matlock the limestone dips to the east beneath the Yoredale Shales and Millstone Grit series which form a small basin and soon dip west, and then roll over in an anticline and dip beneath the east Derbyshire coalfield and Permian rocks.
