Sharp British sandstone
"It's a bloody hard rock" - Derbyshire farmer
Climbers love it as they get good grip, masons love it because it cleans up well and weathers beautifully. Walkers adore it because it makes wonderfully diverse scenery, flour millers love it because it makes even
millstones, traditional toolmakers like it for its even quality when making grindstones.
So what is Millstone Grit? Simply, it is a type of sandstone. The word "grit" is frequently applied to sandstone rocks with more angular particles. The rock is so called because in the English Midlands it was used for making millstones for use in flour mills, as used throughout Britain and Northern Europe. It is a hard, massive and substantial rock, with a variable grain (dependent on the size of the sand grains) whose colour is equally changeable, from pale yellow through gorgeous reds and yellows to a dense, dark grey.
A Brief History of Grit
The majority of Namurian gritstones were formed in the Silesian period of the Carboniferous Age, in wide river valleys or shallow coastal areas, from the rock particles washed off the surrounding mountains. The original rocks were the Cambrian and Pre-Cambrian metamorphic rocks of Caledonia (like those found today in the Scottish Highlands). Evidence suggests that most of the rivers were running south or south-west into low plains, depositing the particles in the valleys to form wide, deep beds, sometimes interbedded with shales formed from finer mud particles.
As the sediments settled, a process of compression and concretion ensured the fine, dense structure of today's millstone grit. Now 310-320 million years later, the rocks give up their story, in the natural beauty of the Dark Peak in the Peak District and the awesome South-western moors and coasts.
The majority of grits from this era are now to be found in three main areas in the UK - in the Southwest, Devon and Cornwall, the Midlands, Staffordshire and Derbyshire up to Lancashire, and a band surrounding Glasgow in Strathclyde. It is known by many names, even in England - Haslingden Flags (from Lancashire), Chatsworth Grit in the Midlands and Yorkshire, and Kinderscout Grit from the Lake District. Similar rocks are of course, known worldwide, often by different names. There are similar rocks in France and the Rhine valley, and in North America the Pottsville Conglomerate is similar.
Quarried for centuries, the grits were valued for their fine quality and stability. Even today, grinding stones and whetstones are made of the finer grades of rock, and in the Peak District, it is frequently used for building, as has been the case since Neolithic times.
A recent trip into Derbyshire revealed how the stone is still in use - from the stone circle of Nine Ladies on Stanton Moor, through the village houses and churches to the flagstones on Bakewell's pavements. Stanton stone is still exported worldwide from quarries in the area, valued for its quality and consistency.
Introducing Geology, D.V. Ager, Faber & Faber, London
http://61.1911encyclopedia.org/M/MI/MILLSTONE_GRIT.htm
http://www.leedsgeolassoc.freeserve.co.uk/millgrit.html
Encyclopædia Britannica
Lots of walking around on it
Thanks to caknuck for his input