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 



