Spent a day with the West Yorkshire Geology Trust sponsored by Pennine Prospects on Friday 21st October to learn something about the local geology.
The short walk we undertook after an overview of the Watershed
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The Rough Rock forms a natural exposure 500m long in crags overlooking the wooded eastern slopes of Loadpit Beck. Scattered exposures of the Rough Rock Flags and the shales below occur in the beck itself. There are many fallen rocks in the slopes below the crags.
Shipley Glen was laid out for recreational pursuits during the Victorian era. There is a long history of use as a park and fairground, which only ceased in the 1990s. The exhibition in the Bracken Hall Countryside Centre adjacent to the site has photos and text documenting the history of the Baildon Moor area.
With a wide range of geological features and the proximity of the Countryside Centre, the site has high potential for educational use. Baildon Moor and its geomorphological and industrial features can be seen from the top of Shipley Glen. There are footpaths in the woods to the base of the crags, so that the sandstone textures and features can be seen easily. Paths to the exposures in Loadpit Beck are narrower and slippery but can still be reached by groups of all sizes.
The whole valley is wooded, so has interesting flora and fauna. There are extensive paths, many of which are very quiet, especially in the upper part of the valley. The views from the top of the crags towards the moors are excellent.
The South Pennines form part of the Pennine ‘backbone’ of England. This narrow range of hills, over 2,000 feet at the highest point, stretches 250 miles from the Peak District of Derbyshire to the Scottish border.
Millions of years ago, when river deltas covered this part of Britain, grit, sand and silt were washed down and deposited here. These became the gritstones, sandstones and shales of the South Pennines. As the conditions changed, these layers were covered by other sediments – forming rocks such as coal.
The Pennines formed in a great upheaval of the rocks, caused by a distant collision of continents. After the uplift, the land may have been as high as the Alps are today! But the softer rocks on top of the Pennine dome were gradually eroded away – once again exposing the harder gritstones beneath.
During successive Ice Ages, great glaciers gouged out wide valleys. As the ice retreated, meltwater torrents continued to deepen some valleys dramatically, leaving side streams to cut their way down steeply to the new valley base below. This abundance of powerful, fast-flowing stream water has had a profound impact on the industrial development of the area.
The South Pennines’ own Millstone Grit and the deposits of limestone left behind by the glaciers have also helped to shape the area’s traditional buildings and industries. They have provided stone to build local farms, homes and mills; rocks to build characteristic drystone walls; and limestone for the production of lime in kilns for use as fertilizer.
Millstone Grit
This term is used for a series of sandstones, siltstones and shales (mudstones) which date from the Namurian epoch of the Upper Carboniferous period and are about 320 million years old. The area that is now northern England lay in a subsiding basin between high mountain ranges. Rivers carried sediments which compressed under pressure of overlying rocks to give a rock sequence which is about 1,700m thick. Deltas of sand built out over deeper waters in which clay and mud was deposited. Sea-level fluctuated because of global temperature changes, so alternating beds of mudstones and sandstones are found. River and delta sediments contain plant fossils, whereas mudstones contain marine fossils, particularly molluscs such as goniatites (like the WYGT logo) and shells.
Coal Measures
After the Millstone Grit rocks were deposited the seas became shallower and deltas built out from the coastlines. Sands and muds brought down by rivers were deposited in huge channels, much like the present Amazon Basin. The continent was close to the equator, so the land surface was covered with luxuriant vegetation, such as tree ferns and other spore-bearing plants. In stagnant lakes and marshes, plant material decomposed without oxygen, so that carbon was retained in the muds. Carbon was locked into coal seams during later burial by sediments. Tree branch and root fossils are very common in river sandstones, whereas marine shell fossils are found in mudstones which were deposited in shallow seas, as sea-levels continued to fluctuate.
Geomap
Stratotable
Permian Rocks
The Permian period followed the Carboniferous period about 290 million years ago. Plate tectonic uplift of southern Europe formed large mountains, so that northern England lay above sea-level in a hot, arid climate. Wind erosion produced blown sand so the first Permian rocks are dune-bedded desert sands called the Yellow Sands Formation, found in a few places in the east of the county. In Late Permian times the land was flooded by a shallow, salty sea called the Zechstein Sea, which dried out regularly because of high evaporation and sea-level fluctuations, leaving precipitated carbonates and other salts behind. The carbonates have been altered to yellow dolomitic limestones during later burial, inter-bedded with reddish mudstones. Fossils are rare, because not many forms of life could survive in such saline waters.
FURTHER READING
Rocks and Landscapes of Huddersfield, available from Huddersfield Geology Group http:/www.huddersfieldgeology.org.uk
Yorkshire Geology by Paul Ensom, 2009, Dovecote Press ISBN 978-1-904-34964-8
Yorkshire Rock by Richard Bell, 1996, British Geological Survey ISBN 978-0-852-72269-5
Sources -
http://www.pennineprospects.co.uk/south-pennines/geology
http://www.wyorksgeologytrust.org/westyorksgeology.html
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