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A Geographical Study of the Diggle Valley ~ Geology

Section 2. Geology

Map4: Rock locations in Lancashire in relation to the area of study.

Map4: Rock locations in Lancashire in relation to the area of study.
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The Diggle Valley is a tributary of the Tame Valley and most of the rocks in the area were laid down during the Carboniferous, Permian and the Triassic eras, the oldest the Carboniferous in the east and the youngest the Permo/Triassic in the west

Map5: The geology of the Pennine region.

Map5: The geology of the Pennine region.
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For the geology for the area of study - The Diggle Valley, see map 6.

Map6: The geology of the area around Diggle.

Map6: The geology of the area around Diggle.
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Most of the ancient rocks are covered by the more recent glacial deposits especially in the low lying land to the west. The River Tame and it's tributaries have cut deep valleys through the rocks of the Millstone Grit Series and in places the overlying coal measures have been exposed.

The oldest rocks exposed are thick gritstones known as the Millstone Grit Series. These rocks comprise of a series of gritstone and sandstones separated by mudstones and shales with a total thickness of about 700 metres. They were formed by a large delta spreading from the north east and gradually infilling the deep marine basin that occupied this region about 280 million years ago.

Diagram1: The cycle involving rivers and deltas.

Diagram1: The cycle involving rivers and deltas.
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The Millstone Grit Series can be divided into three main sections, Middle Grit, Kinderscout Grit, and Shale Grit. The earliest of these rocks – the Shale Grit of Yoredales (consisting of alternating layers of shale and sandstone which can be seen at the base of the Millstone Grit Series) were formed at the top of the delta in somewhat shallower water, whilst the youngest of these rocks, the Middle Grits represent the final infilling of the Central Pennine Basin.

The Shale Grit, consisting of a coarse-grained grits – sandstones with fine-grained shales, form the eastern boundary of Thorns Clough, (see photo 4).

Photo4: Harrop Ridge.

Photo4: Harrop Ridge.
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Photo 4 shows Harrop Ridge which is the eastern boundary of Thorns Clough. It consists of Shale Grit of Yoredale Rock but none of it is exposed. The Shale Grit areas do not attain the same height as the Kinderscout Grits and this is illustrated by the hills in the background of the photograph which are Kinderscout Grit.

The Kinderscout Grits consist mainly of massive coarse grits and this rock has been quarried for millstones, engine beds and massive foundation stones. Some of the finer beds are used for paving stones, road aggregate, flags as well as ordinary building stone and the rock generally retains its colour and is not subject to discolouration by iron stains.

Photo5: Ruins of Intake Farm in Thorns Clough.

Photo5: Ruins of Intake Farm in Thorns Clough.
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Photo 5 shows the ruins of Intake Farm in Thorns Clough, a typical example of the way the Grits were used for building stone and also for the field boundaries.

Photo6: Ladcastle Quarry Uppermill in 1900.

Photo6: Ladcastle Quarry Uppermill in 1900.
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Quarrying scarred many a hillside in Victorian Saddleworth. The workings here at Ladcastle Quarry Uppermill were particularly extensive and supported a large workforce. Photo 6 was taken in 1990.

Photo7: Hillside being exploited by the Quarry at Uppermill.

Photo7: Hillside being exploited by the Quarry at Uppermill.
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Photo 7 shows how the hillside has been exploited by the Quarry at Uppermill.

The Kinderscout Grits also form the grit-stone scarps capping the steep valleys, an example of such a scarp is Harrop Dale Edge - see photo 8

Photo8: The Kinderscout Grit area of Harrop Dale Edge and Hunters Hill.

Photo8: The Kinderscout Grit area of Harrop Dale Edge and Hunters Hill.
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Photo 8 was taken just above Intake Farm looking down Thorns Clough. It shows the Kinderscout Grit area of Harrop Dale Edge and Hunters Hill which form the western boundary of Thorns Clough.

Photo9: An out-crop of Kinderscout Grit on Harrop Dale Edge.

Photo9: An out-crop of Kinderscout Grit on Harrop Dale Edge.
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The lowest measures of this group are known locally as the Grindslow Shales and these consist of mudstones and siltstones with a few inconsistent beds of sandstone and grit, whilst the upper measures consist of coarse grits and sandstone separated by thin bands of silty shales. An excellent example is the Huddersfield Road cutting at Standedge just above the Diggle Valley which shows a number of beds of grit separated from the lower beds by the Butterly Marine Band which is a shale bed containing preserved specimens of marine mussels. Also within these silty horizons are beautifully preserved snail trails called Scolicia on the base of the very thin sandstone.

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Photo10: The Standedge Cutting through the Grindslow Shales.

Photo10: The Standedge Cutting through the Grindslow Shales.
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The Middle Grits are represented in Saddleworth by the formation known as Pule Hill Grit. This rock takes its name from the great triangular hill which stands a short distance to the east of the road cutting through the summit of Standedge.

Photo11: Pule Hill

Photo11: Pule Hill
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They consist of thick beds of sandstone separated by thick beds of mudstone and shale. A number of marine bands may be present in this group of rocks. Marine bands are black Fossiliferous shales representing periodic returns to fully marine conditions and containing an abundance of marine fauna. Although very thin – usually about one metre, they are widespread and may have been used as a marker horizons for correlation with the rest of the British Isles. Other fossils in the Middle Grits include plant fragments such as fern leaves, sections of branches and logs which become more common towards the top of the group heralding the onset of coal-forming conditions. The top layer of the Middle Grit Series is known as Rough Rock and this contains a thin seam of coal. There is no evidence of this being found in Thorns Clough and the nearest is a thin seam which is near to the surface at Thurston Clough at Delph and this is too thin to be of economic value although there have been several attempts to work it – see diagram 2.

Diagram2: Coal-mining and fire-clay getting in the Saddleworth area newpaper clipping.

Diagram2: Coal-mining and fire-clay getting in the Saddleworth area newpaper clipping.
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After the final infilling of the Central Pennine Basin, the shallow water deltaic conditions gave way to vast coal forming swamps similar to those which exist today in the Mississippi Delta. These produce a variety of sediments generally more finer grained than those of the Middle Grit Series and comprise of sandstones, siltstones, mudstones and shales usually of a dark grey colour and almost formed in a fresh water of brackish environment. Occasional minor marine incursion still took place in the early stages of the coal forming period. Some of the more extensive of strata-Westphalian A,B and C in this area. Subdivision within these smaller groups, however, is achieved by the use of non-marine mussel horizons which are common in these rocks although there are no known localities of non-marine bands even with the Tame Valley.

Following the deposition of the Coal Measure Strata there was a major period of earth movements where much of the rocks were folded, faulted and uplifted into mountain chains such as the Pennines and then subject to considerable erosion. The above account of the solid geology has not taken into consideration the effect of superficial deposits which have modified the surface after the Millstone Grit Series were first laid down. There are many places where the bare rock is exposed such as Harrop Dale Edge, but more commonly, however, the bedrock is covered by peat, glacial clays or in the case of Thorns Clough, river alluvium. There are patches of boulder clay to be found on Wharmton Hill to the south-west of Uppermill at a height of more than 1,000ft. This evidence suggests that the ice reached a great depth and covered all but the highest moors around Saddleworth. During the Quaternary or Glacial Period thick ice sheets spread from the west across the Cheshire Plains as far as the foothills of the Pennines which acted as a barrier against any further movements. This halt caused the piling-up of thick deposits of boulder clay as a type of terminal moraine and also the damming-up of numerous lakes in the valleys and foothills. In these lakes were deposited current bedded sands and gravels. During the retreat stage of the ice, the vast amount of water produced by melting resulted in the discharge of large quantities of sand and gravel which being deposited by running water is even, well sorted and current bedded as opposed to the boulder clay which is poorly sorted. The boulder clay varies in composition from a stiff, heavy clay with a few stones to a sandy clay containing many stones. The stones are or various shapes and sizes and vary from small fragments to large boulders and consist of local and far travelled rock-erratics from the Lake District and Ireland showing the vast extent of the ice-sheets. There is very little boulder clay around Saddleworth but the deposits increase in thickness and extent over the lower reaches of the Tame Valley. Although none is found within Thorns Clough, more than half of Saddleworth lies above 1,000ft. and most of the high area is covered by peat. The Peat Haggs are divided by steep gullies formed by the hundreds of miniature watercourses which drain into the valleys. The moorland valleys are known as cloughs and several of these have been dammed back to form reservoirs to supply both Saddleworth and the neighbouring Lancashire towns. Some, such as Brun Clough Reservoir was built to supply to Huddersfield Canal with water.

Photo12: Brun Clough Reservoir which is sited to the north east of Thorns Clough.

Photo12: Brun Clough Reservoir which is sited to the north east of Thorns Clough.
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Many were also constructed to power the local mills – (see Section 4. Industry). Water gathered from the gritstone moors is soft and the acidity arising from the peat can be corrected by addition of small amount of Lime. It is excellent water for the textile industry and although the moors are of little use to agriculture – (see Section 3. Agriculture) they do provide Saddleworth with an important 'export' for good water is a vital raw material in industry. The shale and the grit beds also act as a natural filter and many of the springs are the main water source for some of the hamlets – see photo 13.

Photo13: Spring is at Thurston, Thorns Clough.

Photo13: Spring is at Thurston, Thorns Clough.
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Spring in photo 13 feeds the well in photo 14 which supplies five houses, one farm and a small-holding with their only supply of water. The well is dated 1749 and it is still being used!

Photo14: Well fed by spring at Thurston, Thorns Clough (see photo 13)

Photo14: Well fed by spring at Thurston, Thorns Clough (see photo 13)
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Periodically the water has to be sent for analysis. Diagrams 3 and 4 of the analysis for bacteriological testing in 1986.

Diagram3: Analysis for bacteriological testing in 1986 page 1.

Diagram3: Analysis for bacteriological testing in 1986 page 1.
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Diagram4: Analysis for bacteriological testing in 1986 page 2.

Diagram4: Analysis for bacteriological testing in 1986 page 2.
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The following rock samples (diagram 5) are typical of those found in Thorns Clough and were collected from a small stream at Five Acres, Thurston. The stream flows into Thorns Beck.

Diagram5: Rock samples.

Diagram5: Rock samples.
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Diagram6: A geological cross-section of the valley taken at the same site as the rock samples in diagram 5.

Diagram6: A geological cross-section of the valley taken at the same site as the rock samples in diagram 5.
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Map7: Site of rock sample collection shown in diagram 5. Scale 1:25,000

Map7: Site of rock sample collection shown in diagram 5. Scale 1:25,000
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In 1983, oil fever hit the Diggle Valley! This was the only report in the local newspaper - see diagram 7. I tried to contact the oil companies concerned, the only one still in operation is Moray Petroleum Holdings and Development Ltd. But they were unable to enlighten me regarding the out-come of exploration, so alas, I am still sitting on my five acres just dreaming of what might have been!

Diagram7: Prospectors head for Saddleworth newpaper clipping.

Diagram7: Prospectors head for Saddleworth newpaper clipping.
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