Page:VCH Derbyshire 1.djvu/80

 A HISTORY OF DERBYSHIRE denoted by the trend of the furrows and ridges of the contortions. There have been several good exposures of these gravels in and near Derby. THE UPLANDS It has generally been considered that the uplands of Derbyshire are comparatively free from glacial drift. This is because the subject has received very little consideration at the hands of geologists. The litera- ture is very meagre and is mainly confined to the Geological Survey memoir which has often been quoted in favour of the absence of drift on the tableland and of the transport of erratics in the valley of the Wye to floating ice rather than to land ice. From what is apparently merely negative evidence it has been inferred that the tableland has never been overflowed by ice. Mr. Deeley considered that the Pennine debris was brought by glaciers flowing down the valleys of the Dove, the Wye and the Derwent, but geologists have carefully reserved judgment until some- thing like moraines or evidences of glaciers are found in the valleys. The Bloody Stone near Cromford has been quoted as a doubtful case of a glaciated rock floor. This stone is composed of a quartzose or silicious limestone, and it is more likely that the groovings are either slickenside or part of the rock structure than that they are due to glacial action. But we are no longer dependent on the Bloody Stone as a doubtful wit- ness to the glaciation of the uplands. The presence of a large mass of Boulder Clay near the village of Crich has long been known. About two years ago Mr. Deeley and the writer found that the limestone floor, which had been recently exposed by removal of the Boulder Clay, was finely striated, polished and grooved. The striae ran north 20 west, indicating an ice flow roughly coinciding in direction with the neighbouring Derwent valley. Large masses of drift cover the ground in the neighbourhood of Ashbourne and Tissington. On Spital Hill south of Ashbourne 50 feet of Boulder Clay were sunk through before reaching the Keuper Marl, and the most of the cuttings in the new railway between Ashbourne and Tissington were in Boulder Clay. Near Bakewell, Stanton, Youlgreave and on the dip slope of Riber Hill near Matlock traces of Boulder Clay containing striated blocks of Mountain Limestone, Gritstone, Toadstone, and in a few cases foreign erratics were noticed by the Geological Survey. They considered that the drift came from the west along a gap cutting across the great barrier of the Pennine Chain ; that its path was up the Goyt valley by Doveholes and Buxton and thence down the valley of the Wye ; that a depression or sub- mergence of 1,100 to 1,200 feet converted this pass into a strait and that the foreign erratics found in the drift of the Wye valley were car- ried from the west on floating ice. The occurrence of high level gravels containing marine shells at Macclesfield, Moeltryfaen and other places has been quoted as evidence of a submergence of at least 1,000 feet. On the other hand it is contended with a great deal of reason that the glaciation in north Derbyshire is due to land ice rather than to floating 32