Editing Geology and landscape of Upper Teesdale - an excursion

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Further upstream the sandstone of the Three Yard Limestone Cyclothem forms a low river cliff. This disappears where a fault (the continuation of the Holm Head Vein), downthrowing c. 10 m southeast, cuts the valley in a northeast–southwest direction and results in the repetition of the geological succession so that the second footbridge [NY 947 262] is also sited on the thickest post of the Three Yard Limestone. Around the second footbridge, a c.0.4 m bed of calcareous shale separates the two principal posts of the Three Yard Limestone. As the river bed gradient is the same as the local '''dip''' the stream bed follows the top of the limestone for 150 m upstream where a small fault causes flexure in the top of the upper post.
 
Further upstream the sandstone of the Three Yard Limestone Cyclothem forms a low river cliff. This disappears where a fault (the continuation of the Holm Head Vein), downthrowing c. 10 m southeast, cuts the valley in a northeast–southwest direction and results in the repetition of the geological succession so that the second footbridge [NY 947 262] is also sited on the thickest post of the Three Yard Limestone. Around the second footbridge, a c.0.4 m bed of calcareous shale separates the two principal posts of the Three Yard Limestone. As the river bed gradient is the same as the local '''dip''' the stream bed follows the top of the limestone for 150 m upstream where a small fault causes flexure in the top of the upper post.
  
=== Locality 4 [NY 947 264] ===
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=== Locality 4 [NY 947 264] ===
  
A series of '''tufa'''-depositing springs are associated with this same fault on the western side of the valley. A large mound of tufa from a former lower spring source is known locally as the 'Growing Stone' (Figure 16.1a).
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A series of '''tufa'''-depositing springs are associated with this same fault on the western side of the valley. A large mound of tufa from a former lower spring source is known locally as the 'Growing Stone' (Figure 6. a).
  
 
The calcareous shales upstream provide many well preserved examples of crinoid sections, brachiopods, '''bryozoan''' colonies and occasional fish teeth. Among boulder debris in the beck are examples of exotic clasts derived from the till cover in this valley, including green andesitic volcaniclastic rocks (Borrowdale Volcanic Group) and Shap Granite from the Lake District, as well as locally derived material including clasts of Frosterley Marble.
 
The calcareous shales upstream provide many well preserved examples of crinoid sections, brachiopods, '''bryozoan''' colonies and occasional fish teeth. Among boulder debris in the beck are examples of exotic clasts derived from the till cover in this valley, including green andesitic volcaniclastic rocks (Borrowdale Volcanic Group) and Shap Granite from the Lake District, as well as locally derived material including clasts of Frosterley Marble.
  
Further upstream [NY 948 269] the nature of the Three Yard Limestone Cyclothem changes with non-marine ferruginous shales with '''septarian sideritic''' nodules followed by siltstones, flagstones then a more substantial sandstone that forms the lip of a prominent waterfall.
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Further upstream [NY 948 269] the nature of the Three Yard Limestone Cyclothem changes with non-marine ferruginous shales with '''septarian sideritic''' nodules followed by siltstones, flagstones then a more substantial sandstone that forms the lip of a prominent waterfall.
  
Walking up the Hudeshope valley along the road, the limestones of the succeeding Four Fathom Limestone Cyclothem have been worked in a rather overgrown quarry [NY 949 269] and although somewhat disrupted by faulting these same limestones can be seen forming low cliffs on the west bank of the beck (Figure 16.1a).
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Walking up the Hudeshope valley along the road, the limestones of the succeeding Four Fathom Limestone Cyclothem have been worked in a rather overgrown quarry [NY 949 269] and although somewhat disrupted by faulting these same limestones can be seen forming low cliffs on the west bank of the beck (Figure 16.1a).
  
=== Locality 5 [NY 948 272] ===
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=== Locality 5 [NY 948 272] ===
  
The Four Fathom Limestone is extensively exposed in the river bed upstream of Skears Bridge, where it is also markedly disrupted by '''calcite'''-filled tension gashes associated with mineralized faulting. Higher upstream, the sedimentary sequence between the Four Fathom Limestone and the Great Limestone (Namurian, Upper Carboniferous) is seen in a poorly accessible west-facing river cliff. At Skears Scars [NY 948 276] Hudeshope Beck has cut a spectacular gorge through the Great Limestone which commences on the north side at a well exposed partly mineralized fault with 18 m downthrow to the northeast (Hall's Vein; [[:File:YGS_NORTROCK_FIG_16_1.jpg|Figure 16.1]]a). Beds here and in nearby Skears Quarry [NY 949 272], rich in the solitary coral ''Dibunophyllum bipartitum, ''constitute the Frosterley Marble horizon.
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The Four Fathom Limestone is extensively exposed in the river bed upstream of Skears Bridge, where it is also markedly disrupted by '''calcite'''-filled tension gashes associated with mineralized faulting. Higher upstream, the sedimentary sequence between the Four Fathom Limestone and the Great Limestone (Namurian, Upper Carboniferous) is seen in a poorly accessible west-facing river cliff. At Skears Scars [NY 948 276] Hudeshope Beck has cut a spectacular gorge through the Great Limestone which commences on the north side at a well exposed partly mineralized fault with 18 m downthrow to the northeast (Hall's Vein; [[:File:YGS_NORTROCK_FIG_16_1.jpg|Figure 16.1]]a). Beds here and in nearby Skears Quarry [NY 949 272], rich in the solitary coral ''Dibunophyllum bipartitum, ''constitute the Frosterley Marble horizon.
  
 
Return to the vehicle and leave Middleton-in-Teesdale on the B6277 for Bowlees.
 
Return to the vehicle and leave Middleton-in-Teesdale on the B6277 for Bowlees.

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