The Peak District of Derbyshire is at the southern end of the Pennine 'backbone' of hills which runs up through northern England. The Peak is made up of a limestone upland plateau dissected by river valleys (the 'White Peak') surrounded to the west, north and east by high moor land outcrops of sandstone and shale (the 'Dark Peak').
The core of the Peak District is mostly formed from pale grey, thickly-bedded limestones of Carboniferous age deposited between 350 and 325 million years ago. The limestones form a 'sequence' off strata up to two kilometres thick, although only the uppermost 600m are exposed at the surface.
The White Peak is also made up of limestone, with distinctive pale grey/white outcrops. Deep, narrow, tree-lined valleys (or 'dales') form a drainage network on the limestone plateau. There are also outcrops of volcanic rocks and deposits of dolomite and mineralised rocks.
The limestones were overlain by a succession of Upper Carboniferous sandstones and shales deposited by a giant river delta system between 325 and 315 million years ago. Today the sandstone and shale sequence of the Millstone Grit has been eroded back to form a series of escarpments and moor lands which surround the limestone outcrop.
The Brassington Moor Quarry exploits strata that form part of the Bee Low Limestone Group. These are of carboniferous age and are some 330 million years old. They form one of Europe's purest deposits of natural calcium carbonate.
The rocks were originally deposited in a warm shallow sea, surrounded by much deeper water - very similar to the present day Caribbean. At this time, the United Kingdom would have been located somewhere near the Equator in tropical latitudes. To the north of the quarry location, as far as Buxton and Castleton and eastwards into Lincolnshire, would have been shallow lagoons, only a few metres deep. The area was far from land – no riverborne sediments were present to disturb the slow accumulation of shell and coral debris that over time has been transformed into pure calcium carbonate.
Only the occasional volcanic eruption disturbed this peaceful environment. The thin clay seams that can be seen in a number of quarry faces give evidence of volcanic activity. The volcanoes erupted ash and dust into the atmosphere. These then settled onto the surface of the sea before sinking to the seabed where they formed the thin layers of the bentonite clay we see today.
These seams are known locally as "weyboards", and they can be traced over large distances. The lead miners of previous centuries would use them to locate their stratigraphic position as they moved from one mine to another.
Fortunately for Longcliffe, the lead mineralisation so common to the area has passed us by. No lead, fluorspar or barytes mineralisation is present within our part of the deposit. This is of enormous benefit in maintaining the purity and consistency of our finished products.
Download our Geological Map of Peak District Area. This shows the composition of rocks from Matlock across to the area surrounding our Brassington Moor Quarry.