West Yorkshire (Bradford, Calderdale, Leeds, Kirklees and Wakefield Districts)
The West Yorkshire area is underlain by rocks of Carboniferous age which are tilted gently to the south-east so that the oldest part of the succession occurs in the west. The moors to the west of Bradford and Calderdale are formed in the shales and hard coarse-grained sandstone beds of the Millstone Grit.
These rocks give way to the shale, mudstone and sandstones of the overlying Coal Measures which underlie Bradford and Leeds. The Coal Measures are in turn overlain by the Permian Magnesian Limestone which occurs as a narrow north-south running ridge between Leeds and Tadcaster.
The youngest geological material is that left by the melting of ice over 10,000 years ago during the closing stages of the last Ice Age. This material, called till (or boulder clay), is still soft and consists of sticky clay containing boulders and pebbles.
Carboniferous
Carboniferous rocks (354-290 million years old) comprise nearly all of the solid geology of West Yorkshire and belong to two main series; the Millstone Grit and the overlying Coal Measures. The hard ‘grit’ sandstones and intervening shales of the Millstone Grit outcrop west of Bradford and to the north of Leeds. These rocks were deposited as sediments in a coastal environment where large river deltas were building out into the shallow, tropical marine waters that covered much of Britain at this time. Continuing deposition over the millennia led to the further building out of the deltas and the formation of an extensive low-lying, swampy area in which the succeeding Coal Measures were deposited.
The different rates of erosion in the alternating layers of sandstone and shales of the Millstone Grit have created a scarp and vale topography which is responsible for the switchback nature of many of the routes going north from Leeds. The smooth hills and plateau surfaces formed by the Millstone Grit supports extensive but poorly drained pasture land which is prominent in areas such as Ilkley Moor and Wadsworth Moor. The sandstones of the Millstone Grit have eroded slowly to form prominent crags such as those at Otley, Ilkley and Caley.
In Upper Carboniferous times, the periodic flooding and building of the swamp deltas along the coastline resulted in the deposition of a series of layers of coals (representing the compressed remains of the luxuriant swamp vegetation) interspersed with layers of shale, clay, sandstone and mudstone. These sediments now form the Coal Measures, which overlie the Millstone Grit and form the solid geology underlying the major conurbations of Bradford and Leeds. Fossils within the various layers of the Coal Measures include mainly plants, but also marine shells and animals that lived in brackish water conditions indicating that there were repeated advances and retreats of the shallow sea over the deltas throughout the Upper Carboniferous.
The Lower and Middle Coal Measures contain the once economically important coal seams, together with fireclay and ironstone. The overlying Upper Coal Measures are mainly barren of workable coal seams and are largely composed of red marls, mudstones, siltstones and sandstones.
Permian
To the east, the Coal Measures are overlain by rocks of Permian age. At the base of the sequence are sandstones known as the ‘Yellow Sands’ which represent the remnants of Saharan-like desert sand dunes. The Yellow sands are overlain by cream to buff coloured limestones know as the Magnesian Limestone which forms a west-facing escarpment. The Magnesian Limestone is tougher than the gently folded Coal Measures rocks it rests on, and so erodes more slowly and has left a number of isolated hills (outliers) capped by limestone. The Magnesian Limestone was deposited in a relatively shallow landlocked sea extending from north east England to Poland, known as the Zechstein Sea. The estimated average temperature during the period was approximately 23°C. Due to the landlocked nature of the sea and high temperatures, gypsum and anhydrite (collectively known as evaporites) were produced as the sea water gradually evaporated and today form extensive deposits beneath the floor of the North Sea. Within the Magnesian Limestone the remains of fossil reefs (often including numerous fossil algae, bivalves, gastropods and bryozoans) which grew on the edge of the Zechstein Sea can be found.
Quaternary
Over the last two million years the climate of Britain has varied tremendously with periods of temperate climate interrupted by repeated advances and retreats of glaciers and ice sheets. Collectively these periods have become known as the Ice Age (we are still in one of the temperate phases) and the actions of the ice sheets have been instrumental in forming the landscape we see today.
There is evidence in the Leeds area for two main glacial phases (the Anglian and Devensian) with an intervening temperate (Ipswichian) phase. For both glacial periods it is considered that the ice front lay just to the north of Leeds but impinged upon the vicinity of Bradford. Clay deposits with boulders and pebbles produced through erosion of the underlying rocks by the glaciers (known as till or boulder clay) are present to the north of Leeds and in the Bradford area. The most recent till (from the last glacial; the Devensian) contains blocks of limestone and indicates an origin for the ice from the Yorkshire Dales area while the till from the earlier glaciation (the Anglian, some 400,000 years ago) contains boulders and pebbles indicating ice movement from across the Pennines. Apart from these areas of till, sands and gravels deposited by meltwater streams are common in the lower parts of the valleys of the Aire and Wharfe where they are dug for aggregate from open pits.
Geological Highlights:
- The tough nature of the Millstone Grit sandstone has made it a prized building stone. It has been used in the construction of many of the older buildings in Leeds: Kirkstall Abbey, the Town Hall, Corn Exchange and Mill Hill Chapel being some of the best examples. Extensive workings used to exist at Bramley, Newlay, Horsforth, Meanwood and Weetwood. The only quarry working the stone today is at Bramhope.
- Coal Measures sandstones, notably the Elland Flags, provides the highest quality of building stone and this was extensively used during the rapid growth of the large conurbations of Bradford, Halifax and Huddersfield. These products, along with the plentiful streams, and local resources of ironstone and coal, have fuelled the long history of industrial development of the area, based on wool, textiles, cutlery and steel.
- The Magnesian Limestone has been worked from small quarries for use as a building stone and to be burnt for lime for agricultural purposes. The stone has not only been used locally in villages such as Bramham and Aberford, but has been worth transporting considerable distances. Stone for much of York Minster was obtained from a quarry near Sherburn and it was also used in the construction of Eton School.
- In 1851, workmen digging clay in a brickworks at Wortley, Leeds, discovered several large bones of such dimensions that "made them think they could not be Christians' bones". As a result, they were brought to the attention of Mr Henry Denny, Curator of the Leeds Philosophical and Literary Society's Museum, who identified them to be bones of the Great Northern Hippopotamus. Denny gathered numerous bones and teeth which enabled him to identify the animals. There were the part remains of three hippopotami - an aged individual and two adults - an elephant and an auroch (extinct wild ox). Later research identified the animals as Hippopotamus amphibius, Elephas primigenius and Bos primigenius. Dating the remains has proved problematic, but after several tests it was determined that the animals must have lived during the Ipswichian temperate period (approximately 120,000 years ago) of the Quaternary. The hippo is now used as the logo for the Leeds Geological Association.
- The geology of the West Yorkshire area has been paramount in the industrial development of the area. Coal production is, after textile manufacture, probably the most famous West Yorkshire industry. Coal was mined in quantity in West Yorkshire from the medieval period. By 1850, technical improvements allowed the extraction of more coal out of deeper seams. By the end of the 19th century, there were nearly one hundred individual coal mines in West Yorkshire, mostly in the east of the county. Coal mining was often associated with ironstone and clay extraction. The clays were used in pottery production. The larger potteries tended, from the late 18th century, to be concentrated in Leeds and Castleford, however, small local potteries were scattered throughout the county in the mid to late 1800s. Glass manufacture was also mostly localised in Leeds and Castleford.
Local sites
The following localities represent, in part, the geology of this county. Each locality has a grid reference, a brief description of how to get there and a short summary of the geology you are likely to find. All the localities listed are openly accessible.
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