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Volume 03: Caledonian Structures in Britain South of the Midland Valley
 

Figure 1.1
Regions of the Caledonian–Appalachian Orogen in their pre-Mesozoic drift configurations, showing ages of principal deformation events (after Barker and Gayer, 1985).

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Figure 1.2
Schematic cross-sections of the Caledonides, after Dewey (1969, Figure 2E and F). (A) represents Iapetus during the Silurian. (B) shows the situation after collision in the early Devonian, with ornament indicating fold style in Lower Palaeozoic rocks. Black areas represent volcanics and intrusions of the Ballantrae Complex (NW) and Gwna Group of Anglesey (SE); Vs represent Upper Ordovician volcanics of the Lake District and Wales.

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Figure 1.3
Simplified map of the British Caledonides, modified from Leake et al. (1983).

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Figure 2.1
Geological map of the Southern Uplands, showing the distribution of the three main belts, some of the steep faults that bound these belts, and subsidiary tracts. The positions of the sites discussed are also shown. A and B, in the south-west, show the zones of D2 folding and steep D1 plunge respectively, as discussed in the text.

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Figure 2.2
Cross-sections of the Southern Uplands. (A) After Lapworth (1889); (B) after Walton (1961); (C) reconstructed profile of the accretionary prism, in Wenlock times. The tracts 1–10 are of decreasing age south-eastward, within each tract rocks young to the north-west. The style of the D1 folding is shown schematically in the Llandovery and Hawick Rocks of the Central Belt (after Leggett et al., 1979).

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Figure 2.3
Siccar Point. Subvertical Silurian greywackes and cleaved shales on the south limb of a tight Caledonian syncline are unconformably overlain by Upper ORS breccias and sandstones. View looking east with lens cap (centre) for scale. (Photo: J. Roberts.)

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Figure 2.4
Geological map of Agate Point (after Dearman et al., 1962).

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Figure 2.5
Diagrammatic representation of the folds at John’s Road (after Dearman et al., 1962).

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Figure 2.6
(A) Diagrammatic fold profile of the Knockbrex Bay–Kirkandrews Bay coast section, with box indicating the location of the Barlocco site. Approximate position of the folds illustrated in (B) is also shown. (B) Typical fold and cleavage geometry at the Barlocco site, based on field observations at NX 5835 4865. Cleavage is shown: open spaced in sandstones and narrow spaced in mudstone. Plunge of fold hinges and cleavage – bedding intersections are also shown (after Stringer and Treagus, 1980, Figure 2).

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Figure 2.7
Cruggleton Bay North. D1 folds in Silurian siltstones and mudstones, plunging to the south-west, transected by non-axial plane cleavage (parallel to hammer). (Photo: P. Stringer.)

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Figure 2.8
Cruggleton Bay. (A) Location map showing position of Folds A, B, and C. (B) Schematic diagram of Fold A, drawn from field sketches, showing relationship of cleavage (dashed) to the folded greywackes (dotted). F = finite neutral point.

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Figure 2.9
Sketch of the Isle of Whithorn Bay site.

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Figure 2.10
Typical fold plunge variation in Hawick Rock greywackes. This pericline, viewed from the north-west, is at Shaddock Point (NX 478 393), near the Isle of Whithorn site. (Photo: P. Stringer.)

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Figure 2.11
Typical cleavage refraction from mud/siltstone to sandstone seen in Hawick Rocks in profile view; in plan view cleavage transects the fold hinges. Locality: Port Allen (NX 478 411), near Isle of Whithorn. (Photo: P. Stringer.)

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Figure 2.12
West Burrow Head. (A) Geological map of site. (B) Sketch cross-section along line A–B of Figure 2.8A).

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Figure 2.13
Type-D1 syncline in massive Silurian greywackes, Back Bay, Monreith. View to the north-east, with figure for scale. (Photo: J. Treagus.)

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Figure 2.14
Sketch of the Back Bay site, drawn from photographs. Horizontal scale is not linear; total length is approximately 200 m.

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Figure 2.15
Geological map and cross-sections (inset) of the Grennan Bay site (after J. A. McCurry, unpublished).

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Figure 3.1
Geological map of the Lake District, and Cross Fell and Craven Inliers, showing lithostratigraphical groups, and major folds and faults of Caledonian age (adapted from Moseley, 1972; Branney and Soper, 1988).

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Figure 3.2
Cross-sections along lines shown in Figure 3.1 (modified from the work of N. J. Soper in Johnson et al., 1979).

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Figure 3.3
The cleavage arc in the Silurian rocks of north-west England, showing cleavage transection data for the Crook area, eastern Howgill Fells and Ribblesdale Inlier (after Soper et al., 1987).

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Figure 3.4
Skiddaw Group exposures, near Buttermere. (A) is horizontal surface. (B) Vertical roadside section in (A) looking towards 060@o. Three fold phases are represented in these exposures. The steep plunge of the folds represents the dip of a limb fold, initiated during F0. The D1 phase is represented by the tight ENE–WSW folds and related cleavage, and D3 by open recumbent folds and crenulation cleavage which can only be viewed on vertical surfaces, where the other two phases cannot be seen (after Moseley, 1981, and notes by D. Aldiss B.Sc. thesis, Birmingham University, 1974).

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Figure 3.5
Hassness and Goat Crags. Sketch view from the south-west, showing outcrop pattern and axial-plane traces. Length of foreground is approximately 500 m.

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Figure 3.6
Goat Crag, Buttermere. Slump-generated minor folds on the inverted limb of a major slump fold in the Skiddaw Group (hammer for scale, middle right). (Photo: Courtesy of the British Geological Survey, D 3843.)

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Figure 3.7
Goat Crag, Buttermere. The sandstone lens is part of a slump-generated melange which has been folded by minor D1 folds with a poorly developed axial-planar cleavage. (Photo: Courtesy of the British Geological Survey, D 3849.)

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Figure 3.8
Geological map of the Gasgale Crags and Whiteside area, based on Geological Survey map (NY 12 SE) surveyed by P. M. Allen, A. H. Cooper and B. C. Webb (see also Moseley, 1990, Figure 20).

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Figure 3.9
Structural map of the River Caldew section, showing the main folds in the hornfelsed slates of the Skiddaw Group. Inset diagrams are enlargements (x4) of selected localities, each with an accompanying equal-area projection of the structural elements of that locality (after Roberts, 1971). Localities A–D referred to in text.

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Figure 3.10
River Caldew. Steep NE-plunging folds in hornfelsed slates of the Skiddaw Group produced largely by gravity-driven slumping. They show the truncations and variable, disharmonic style typical of this process. Bedding planes are chalked (compass top right for scale). (Photo: D. Roberts.)

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Figure 3.11
Map of the structures in the Loweswater Formation on Raven Crags, Mungrisdale. A–B and C–D are the lines of the cross-sections illustrated in the inset (modified from Roberts, 1977b).

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Figure 3.12
Detailed map and sections of the Skiddaw Group–Borrowdale Volcanic Group junction exposed in Warnscale Bottom. Anticlines, synclines, dip of bedding and cleavage are shown (after Moseley, 1975).

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Figure 3.13
Geological map of the junction between the Borrowdale Volcanic Group and the Skiddaw Group in the area around Grange-in-Borrowdale, Cumbria, showing localities mentioned in the text.

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Figure 3.14
Geological maps illustrating the nature of the faulting in three areas within the Limestone Haws–High Pike Haw, Coniston site (after Moseley, 1990, Figure 52B, C and D). (A) South side of Little Arrow Moor. (B) Area around Torver Quarry. (C) Area around Ashgill Quarry.

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Figure 3.15
Structural map of the Ulpha Syncline at Torver High Common (after Soper and Numan, 1974; Soper and Moseley, 1978, Figure 24).

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Figure 3.16
Geological map of the Bannisdale Syncline, showing positions of Crookdale Crags (see Figure 3.17) and Jeffrey’s Mount (after Moseley, 1986).

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Figure 3.17
Fold structure along A6 road-cuttings at Crookdale Crags, Shap (after Moseley, 1968).

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Figure 3.18
Shap Fell. D1 folds developed in Silurian greywackes; cleavage can be seen in the interbedded muddy siltstone. View to east. (Photo: J. Treagus.)

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Figure 3.19
Fold structure at Jeffrey’s Mount, Tebay (after Moseley, 1972).

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Figure 3.20
Stereographic representation of data from Helwith Bridge. Poles to bedding (crosses) numbered across the anticline with corresponding numbers at bedding – cleavage intersections (open circles).

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Figure 3.21
Jumb Quarry. The deformed accretionary spheres of volcanic ash have been used to measure the Caledonian strain in these Ordovician rocks. The cleavage plane photographed is 30 cm high and shows the intersection of bedding plunging to the left. (Photo: Dept of Geology, Manchester University).

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Figure 3.22
Flinn plots of average lapilli shapes (A) and actual strain ellipsoids (B) for accretionary lapilli horizons within the Borrowdale Volcanic Group. Ellipsoid long, intermediate, and short axes are denoted by x, y, and z respectively. (A) shows the range of overall lapilli shapes throughout the Borrowdale Group (data from Bell (1981 – open circles), Oertel (1971 – open squares), Green (1917 – solid squares) and Helm and Siddans (1972 – solid triangles). (B) Bell (1981) resolved compaction strains (squares) and tectonic strains (circles). Compaction strains are uniaxial (X = Y) > Z, k tends to zero) whereas tectonic strains are almost plane (k = 1) (data from Bell, 1981).

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Figure 4.1
Map showing the traces of the principal folds and faults of Caledonian age in Wales. The localities described in the text are also shown.

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Figure 4.2
Section through the major folds of Snowdonia (after Wilkinson, 1988).

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Figure 4.3
Alexandra Quarry. (A) Site map, showing Localities A–C described in the text. (B) Sketch illustrating anticline in Dorothea Grit with a faulted south-east limb. See text for explanation. Locality B of Figure 4.3A.

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Figure 4.4
View of Trum y Ddysgl looking south-west. Redrawn from Roberts (1979), after Shackleton (1959).

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Figure 4.5
Cwm Idwal, Gwynedd. The right- and left-sloping slabs above the central scree form the syncline hinge of one of the major Caledonian fold structures in Snowdonia, in Ordovician sediments and volcanics. View to south-west, cliff is approximately 300 m high. (Photo: S. Campbell.)

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Figure 4.6
Cwm Idwal. Geological map showing the positions of Localities A–F described in the text.

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Figure 4.7
Cwm Idwal. (A) ‘Out-of-syncline’ flexural slip and tension gash arrays in the Idwal Syncline. (B) Combination of en bayonet bedding-parallel veins and tension gashes, south-east limit of Idwal Syncline (Locality A).

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Figure 4.8
Geology of the Ogof Gynfor site.

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Figure 4.9
Rhosneigr, Anglesey. Tight minor folds in thin sandstones exemplify the intensity of the deformation in north-west Wales. The enclosing slates have been the subject of studies on the nature of slaty cleavage and strain variations around folded layers (penknife, centre, is 6 cm long). (Photo: J. Treagus.)

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Figure 4.10
Equal-area stereographic projection of the plunge of minor fold axes at Rhosneigr. The site measurements are represented by the head of the arrow, and are divided into three subareas; circles = central, squares = NE and @Vs = SW.

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Figure 4.11
Rhosneigr. Line-drawing illustrating the strong cleavage refraction associated with the hinge of a meso-scale fold delineated by sandstone surrounded by pelite. A photograph of this fold appears in Ramsay and Huber (1983, Figure 10.18).

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Figure 4.12
Cwm Rheidol. (A) Section along track showing bedding attitudes in siltstones and mudstones. Parts (B), (C) and (D) are equal-area stereographic projections of poles to bedding, poles to cleavage, and cleavage – bedding intersections respectively. (B) Dashed lines show great circle and small circle limits of the distribution and the large filled circle gives the pole to the great circle. (C) Dashed line represents mean cleavage attitude. (D) The two mean plunges of the cleavage – bedding intersections (open circles) can be seen to lie on the mean cleavage of (C) as do the pole to the bedding readings in (B).

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Figure 4.13
Allt Wen. (A) shows the relative positions of Localities 1–6 and sketches of the structures described in the text. Total length of the section is approximately 250 m. (B) Thrust seen at Locality 5 (after Cave and Hains, 1986, Plate 23; Fitches et al., 1986, Figure 4C). (C) Thrust and hanging-wall anticline seen at Locality 3 (after Fitches et al., 1986, Figure 4D).

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Figure 4.14
North Clarach. Fold–cleavage–fault relationships on wave-cut platform (modified from map produced by R. Johnson, University College of Wales, Aberystwyth, 1977). Localities 1–4 referred to in the text.

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Figure 4.15
Craig y Fulfran. (A) Regional deformation folds with early asymmetrical small-scale folds on the north-eastern limb, further illustrated in (B) and (C). (B) shows cleavage fans and (C) saddle-reefs in hinge zones (after Fitches et al., 1986, Figures 6A, C and B).

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Figure 4.16
Ponterwyd Quarry. (A) Plan of quarry showing the three localities described in the text. (B) Locality 2; steeply dipping bedding and subparallel slaty cleavage deformed by recumbent second-phase chevron folds and kink bands (after Fitches, 1978, Figure 1). (C) Locality 3; saddle-reefs and tension gashes (after Fitches, 1972, Figure 2).

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Figure 4.17
Ca’er-hafod. Part of the quarry showing bedding dipping steeply south, and cleavage gently north. The outcrop of the central vein (top left to centre) shows minor folds plunging towards the observer, and ridge-and-groove lineation almost at right-angles to this. View looking east. (Photo: R. Nicholson.)

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Figure 4.18
View looking west at Ca’er-hafod Quarry (Llangollen) showing steeply dipping Wenlock country rocks and spar beds (veins).

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Figure 4.19
Sketch section illustrating the structure of the Devonian rocks on the north side of Lligwy Bay.

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Figure 4.20
Lligwy Bay, Anglesey. Strongly developed, spaced cleavage in ?Devonian siltstones dips to the north in the hinge of a south-facing monocline. (Photo: J. Treagus.)

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Figure 4.21
Carmel Head, Anglesey. Figure standing on the low-angle fault plane which has thrust Precambrian schists over Ordovician shales. (Photo: J. Treagus.)

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Figure 4.22
Geology of the Carmel Head site.

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Figure 4.23
Geological map of the main Llanelwedd Quarry with inset summary of main kinematic zones (after Woodcock, 1987b).

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Figure 4.24
Structural map of Strinds Quarry with inset stereogram showing modal orientations of strike-slip and dip-slip faults (after Woodcock, 1988).

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Figure 4.25
Structural map of Dolyhir Quarry with inset stereogram showing modal orientations of strike-slip and dip-slip faults (after Woodcock, 1988).

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Table 3.1
Deformation sequences in the Lake District as interpreted by various authors; the last column shows the system adopted in the present volume.

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