GEOLOGY on the hilltops. An inlier may also form the summit or crest of a dome from the top of which the higher beds have been removed. The largest mass of the Mountain Limestone forms an irregularly shaped inlier, measuring about 20 miles from north to south and 10 miles from east to west. In addition to this there are seven small inliers, viz. at Ashover and Crich on the east, at Kniveton and near Snelston on the south-west, and at Ticknall, Calke and Diminsdale in the southern part of the county. The large inlier is a pericline or dome, the longer axis ranging north-north-west. The beds dip away from the centre of the mass in every direction, and generally speaking the dip at the edges is at right angles to the boundary which is partly natural and partly faulted. A closer examination of the limestone area shows that this concep- tion of a simple pericline must be modified and that it is made up of a number of smaller domes and basins. The three promontories in the limestone on the east, and on which Stoney Middleton, Bakewell and Matlock Bath are situated, are portions of minor domes, whilst the bay in the limestone near Ashford which is occupied by the Yoredale Shales, and the still larger one containing the Stanton outlier of Kinder Scout grit, represent basins in the limestone. So that a section drawn nearly north and south from Eyam to Carsington would show at least three anticlines and two synclines. A parallel section on the west would show at least two anticlines and one syncline. The dip on the east is generally gentle whilst that on the west is greater. The beds near the centre of the area are often horizontal, but on the west both the Mountain Limestone and the Yoredale Shales are thrown into numerous folds. The limestone is the oldest rock in Derbyshire. Its thickness is unknown, the basement beds not having been reached. The section along the Midland Railway between Monsal Dale and Buxton is supposed to show a thickness of 1,600 feet. Between Winster and Grange Mill it has been estimated that at least there are about 2,300 feet thickness of limestone and its associated igneous rocks. It is probable that a greater depth than 2,000 feet has not been reached, and that the lowest beds are those at Grange Mill near Matlock or in the valley of the Wye near Pig Tor Tunnel. The Mountain Limestone varies in structure, composition and colour. It is often an almost pure carbonate of lime, white or light blue in colour, and breaks with an irregular and sometimes conchoidal fracture. The dark grey and black varieties often contain bituminous and argillaceous material. The upper beds of limestone are generally thin and contain numerous bands and lenticles of chert, though chert is by no means confined to the upper beds. Silicified corals, foraminifera and encrinite stems are often found in the chert, and the casts and stems of the latter fossils are locally known as ' screws.' The limestone is distinguished by its fossil contents. Productus encrinites and corals are perhaps the most common. The polyzoa are 5
