GEOLOGY 



SANDS AND FIRECLAYS 



In the neighbourhood of Newhaven and Brassington deposits of 

 sand and clay with quartzite pebbles occur in pockets or irregular hol- 

 lows in the Mountain Limestone. They are situate on a line running in 

 a direction from north-west to south-east for about 7 miles from near 

 Hartington on the north-west to Brassington on the south-east. The 

 clay from the latter place was worked previous to 1789 and used at the 

 Derby Porcelain Works in the manufacture of china. At Minning Low, 

 Longcliffe, Harboro' and Newhaven the sand is made into fire-bricks. 

 The hollows in the limestone are sometimes as much as 100 yards across 

 and probably represent large swallow holes. The sand consists mainly 

 of well rounded quartz grains and is often bedded in the form of a basin, 

 that in the centre of the pit being nearly horizontal and that near the 

 edges dipping steeply away from the limestone which forms the sides. 

 The limestone is often dolomitized. The pits contain in addition to the 

 sand and pebbles fragments of shale, lignite and grit. 



These deposits have been supposed by some geologists to have 

 originated from the millstone grits and by others from the Bunter beds. 

 Probably both suppositions are correct. The shale, grit, Bunter pebbles, 

 sand and clay may represent the products of decomposition of Carbon- 

 iferous and Triassic rocks which have been washed into the swallow 

 holes. There is undoubted evidence that the deposits are preglacial. 



A few words of description may be given of the small inliers of 

 limestone. 



At Ashover, about 4 miles north-east of Matlock, is a small inlier 

 of Mountain Limestone with a bed of intercalated volcanic tuff. An 

 anticline passes through Ashover in a north-north-west direction. The 

 river Amber has cut its way along this anticline down the Millstone 

 Grits, Yoredale Shales, and part of the Mountain Limestone into a bed 

 of tuff which may be seen in the bottom of the valley. In a direction 

 northwards from Ashover the succession of rocks from the limestone to 

 the Coal Measures are passed. 



At Crich the Mountain Limestone has been brought up by three 

 faults and bending of the strata. The inlier of limestone is about a mile 

 in length and consists of an elongated dome the main axis of which runs 

 north-north-west and south-south-east. On the east the beds dip gently 

 under the Yoredale Shales, but on the west they are more highly inclined 

 and faulted against the Chatsworth Grit of Coddington Park. A lava 

 flow contemporaneous with the limestone is found some distance below 

 the quarry floor in some of the old lead mines. Several landslips have 

 occurred. They were due to the slipping of the limestone over a bed of 

 shale in consequence of the quarrying operations which removed some 

 of the limestone occupying the lowest part of the arch. 



Near Kniveton is another inlier of Mountain Limestone. The 

 boundary has not been yet accurately determined because of the 

 covering of the ground by glacial drift. A coarse agglomerate which 



