GEOLOGY 



Erewash valley. South of the Trent it is found at Repton and Fore- 

 mark. In the neighbourhood of Ashbourne the Bunter is much obscured 

 by drift, and its boundary is somewhat uncertain. The uncertainty of 

 arriving at the true boundary of rocks in a country covered by a mantle 

 of drift is exemplified in the district immediately south of Ashbourne. 

 A well was sunk for the Ashbourne waterworks on Spital Hill where 

 the ground was mapped as Bunter by the Geological Survey. But 

 70 feet of drift and over 60 feet of Keuper were passed through before 

 the Bunter beds were reached. Though the Bunter is seen at the surface 

 at many places it is not always present under the Keuper. At Snelston 

 Common the Keuper Marl rests on the Mountain Limestone, and at 

 Mickleover a borehole passed from the Keuper into the limestones and 

 shales of the Yoredale series ; whilst at Derby, 4 miles distant, another 

 borehole indicated that the Bunter was probably present under the Keuper. 

 The Bunter Sandstone consists of a soft yellow and light red sandstone with 

 scattered pebbles mostly of quartzite. The proportion of pebbles to 

 sand varies considerably. Where the pebbles are numerous the rock 

 becomes a gravel with little sand and when hard a conglomerate. The 

 Bunter in Derbyshire is considered to belong mainly to the pebble beds 

 or conglomerate, the Lower Mottled Sandstones being absent except at 

 Dale. Good exposures of the Bunter beds are seen at Ashbourne, where 

 they are at least 120 feet thick. The road from Ashbourne to Clifton is 

 cut through beds of a soft yellow and light red sandstone containing a few 

 pebbles. These measures are also seen in the banks of the old Derby 

 road south of Ashbourne, at Bradley Wood and near Sandybrook Hall. 

 At Brailsford, 23 feet of the pebble beds are exposed in a quarry, and 

 the conglomerate is well exposed on the road from Repton to Ingleby. 

 Near Sandiacre the rock is quarried. It consists mainly of a soft yellow 

 and light red rock with few pebbles. Some of the beds are sufficiently 

 hard to require blasting, but soon become friable. The sand is used 

 largely for building. 



The Keuper beds (or New Red Marl), which overlie the Bunter, are 

 in this district divided into the Red Marl and the Waterstones or White 

 Beds. They occupy a large tract of county south of Ashbourne, Mug- 

 gington, Breadsall and Sandiacre, and stretch across the southern part of 

 the county in a direction from east to west. On the west and south 

 they are bounded by the Dove and the Trent, and on the east by the 

 Erewash. The Upper Keuper consists of beds of red marl and shale, 

 with intercalations of greyish, sandy and micaceous shales or sandstones 

 (called skerry) and irregular bands of gypsum, a hydrated sulphate of 

 lime. The marl is largely used for making bricks and forms a stiff soil 

 well suited for agricultural purposes. The gypsum, which is burnt for 

 making plaster of Paris, occurs in irregular beds, spheroidal masses, 

 lenticular intercalations and veins in the marl. The beds thin out and 

 come in again in a short distance, and vary in thickness and quality. At 

 Chellaston and Aston the gypsum occurs in a bed about 10 to 15 feet 

 in thickness. At the latter place it is worked underground. A tough 



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