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 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