How is millstone grit formed

Its occasional coal-seams show that conditions of coal-formation had already begun. In Great Britain its outcrop extends from the Bristol Coalfield through South and North Wales to its fullest development in the north-midland counties, Lancashire and Yorkshire, and thence to Scotland, where the Roslin Sandstone of the Lothians and the Moor Rock of Lanark and Stirling are considered its equivalents.

Characterized by grits and sandstones of the same general type, though individually variable, as sandbanks formed on the shoaling of the Carboniferous sea, yet often persistent over wide areas, the formation, estimated as ft. Its precipitous northern edge overlooks Ilkley and Lower Wharfedale but there are extensive views beyond, especially from the highest part of the moor that rises to metres.

The edge is formed by the Addingham Edge Grit, a hard, coarse-grained sandstone, commonly called gritstone, similar to sandstones of the Millstone Grit Group that form escarpments flanking many valleys right across the Pennines. The sand that forms this resistant rock was originally laid down on shifting sandbanks in a great river about million years ago during the Carboniferous Period.

Subsequently, the sand was buried by later overlying sediments perhaps to a depth of about 5 kilometers where it was subjected to great overburden pressure and stress from the collision of tectonic plates turning it slowly into hard sandstone. Then, further intermittent earth movements caused uplift and the overlying rocks were slowly removed by wind, water and ice erosion until the sandstone was again exposed at the surface as it is today.

An area famous for climbing, the area was also quarried for grindstones. These rocks were formed in in vast river deltas that once covered the whole of the White Peak from the Roaches in the West to Kinder Scout in the north. The Peak District is dominated by a series of sedimentary rocks that formed million years ago, in the Carboniferous Period. This sedimentary succession began with the deposition of limestone when the Peak District was submerged beneath a warm, shallow sea.

Britain at that time was located on a palaeocontinent near to the equator, and the shallow sea abounded with life, with shellfish, crinoids and fish all living in vast coral reefs. It is in these conditions that limestone forms. Corals, shellfish, snails and eggs all have hard parts formed from calcium carbonate CaCO 3 , a mineral which exists in solution in the oceans.

Animals with hard shells and bones use dissolved CaCO 3 in sea water to form their hard outer shells and bones. Where ocean life is abundant, the skeletal matter collects on the sea floor as organisms die and sink to the bottom of the water column.

This accumulation of material creates limestone. During the Carboniferous, a supercontinent in the South made up of modern-day Africa, Australia, India and South America, Gondwana, was moving due to the activity of plate tectonics and passed close to the South Pole. This caused the build-up of a large continental ice sheet on Gondwana. The buildup of ice on the supercontinent reduced the amount of water in the oceans which caused a global drop in sea level.

This is a piece of branching plant matter. What could be a lovely leaf remain of a fern. Another example of plant stem, possibly more of calamites suckowi. We always find it exciting to find fossils, and we have never come across an abundance of great plant remains so it was definitely worth the slog up the hill!

There are probably lots more to find, but most of the sandstone blocks that have fallen from the quarry faces have been badly weathered so it is hard to really see anything.

I am sure we shall return again to look for more and perhaps we will be lucky and have a few more fresh faces to look at! Lovely views from the top. Background Brimham Rocks are formed of Millstone Grit, which is made from sand, grit and rounded pebbles of quartz and some feldspar.

Geological History The Millstone Grit was deposited as part of a vast river delta system, formed where the river met an ancient sea. The structures we found… Graded Bedding Within most of the rocks you can find examples of graded bedding, where the grains in each layer are coarser at the base and become progressively finer towards the top, as in the image below. Trough cross-bedding structures Ripple structures In the photo below you can see a cross section of symmetrical ripple marks that formed under bi-directional flow regimes, typically associated with beach and shallow marine environments.

The formation of the unusual stone sculptures The outcrops at Brimham Rocks occur in unusual and often disproportioned shapes such as the example in the photo below. Beautiful example of the workmanship at the reservoir What were they mining? Close up of the sandstone Awesome fossils!

Layers of mudstone, with thin beds of sandstone is where we found all the trace fossils The first level of the quarry The finer muddy layers were full of trace fossils, some of which can be seen in the pictures below.

Lots of squiggly lines here which would have been made by creatures roaming around It is hard to see, but you can just make out the almost horseshoe shape imprint of lots of possible leg marks Within the sandstones we were lucky enough to come across some what looked to be recent rock falls which presented to us some brilliantly preserved plant material.

Possible fossil of calamites suckowi This is one of the sample we were able to take back with us What the tree was like We also found an example of Stigmaria ficoides which is a type of branching tree root fossil found in carboniferous rocks.

We think this is an example of Stigmaria ficoides What it would have looked like These are some more examples of fossilised plant remains we found, but they are tricky to properly identify. What could be a lovely leaf remain of a fern Another example of plant stem, possibly more of calamites suckowi We always find it exciting to find fossils, and we have never come across an abundance of great plant remains so it was definitely worth the slog up the hill!

Geological discoveries and interpretations by two young geologists living in Britain. Follow Following. Our Geological Adventures Join 29 other followers.

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