https://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&feed=atom&action=historyDob's Linn, Moffat - an excursion - Revision history2024-03-29T15:43:39ZRevision history for this page on the wikiMediaWiki 1.41.0https://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=23855&oldid=prevJenniferFindlay1 at 11:40, 9 December 20152015-12-09T11:40:11Z<p></p>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>=== Introduction ===</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>=== Introduction ===</div></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Some 19 km north-east of Moffat lies Dob's Linn, a spectacular gorge and waterfall deeply cut into the Ordovician and Silurian shales and greywackes of the Southern Uplands. The well-exposed, virtually continuous Caradoc to Llandovery sequence of graptolite-bearing strata, with its intercalated 'barren beds' was distinguished in the classic researches of Charles Lapworth (1878)<ref>Lapworth, C. 1878. The Moffat Series. Quart. J. Geol. Soc. Lond. 34, 240-346. Lapworth, C. and Wilson, J.1870. The Lower Silurian rocks in the neighbourhood of Galashiels. Trans. Edinb. Geol. Soc. 2, 46-48.</ref> as 'the only section of the Moffat Series which allows us to determine with certainty the sequence and palaeontological characteristics of its component beds, and at the same time exhibits the relationship of the group as a whole to the surrounding greywackes'. Dob's Linn was named after a Scottish Covenanter, Halbert Dobson, who hid from the English Dragoons in the small cave above the waterfall. It is an easily accessible section and abundantly fossiliferous, though at certain critical exposures the visitor is asked to refrain from hammering. Dob's Linn has been the subject of much research (Lapworth 1878<ref>Lapworth, C. 1878. The Moffat Series. Quart. J. Geol. Soc. Lond. 34, 240-346.</ref>, 1970<ref>Toghill, P. 1970. Highest Ordovician (Hartfell Shales) graptolite faunas from the Moffat area, south Scotland. Bull. Br. Mus. Nat. Hist. (Geol.) 19, 1-26.</ref>, Williams 1982-88)(see list in Bibliography below) and is now renowned as the global boundary stratotype for the Ordovician/Silurian boundary (Williams & Ingham 1989)<ref>Williams, S.H. and Ingham, J.K. 1989. The Ordovician-Silurian Boundary Stratotype at Dob's Linn, southern Scotland. In Holland, C.H. and Bassett, M.G. (Editors). A Global Standard for the Silurian System, Nat. Mus. Wales, Geol. Ser. 9, 27-35.</ref>. This lies within a black shale sequence (the Moffat Shale Group) extending from the peltifer graptolite zone of the early Caradoc(Ordovician) to the maximus subzone of the late Llandovery (Silurian). Interbedded volcanic ash horizons are common; Merriman and Roberts (1990)<ref>Merriman, R.J. and Roberts, B. 1990. Metabentonites in the Moffat Shale Group; Southern Uplands of Scotland; geochemical evidence of ensialic marginal basin volcanism. Geol. Mag. 127, 259-271.</ref> describe 135 metabentonite beds cumulating to about 6 m and representing up to 20% of the strata in some biozones (Figure 41). Following Lapworth the Moffat Shale Group is divided into four units with informal formation status: in ascending stratigraphic order these are the Glenkiln Shales, the Lower Hartfell Shales and Upper Hartfell Shales and the Birkhill Shales. The latter are abruptly but conformably overlain by greywackes of the Gala Group, locally assigned to the Queensbury Formation.</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Some 19 km north-east of Moffat lies Dob's Linn, a spectacular gorge and waterfall deeply cut into the Ordovician and Silurian shales and greywackes of the Southern Uplands. <ins style="font-weight: bold; text-decoration: none;">[[File:P571542.jpg|thumb|300px|left|View towards Dob's Linn, Moffatdale, Main Branch round spur on right, Linn Branch on left in from of red scar. P571542]][[File:P772042.jpg|thumb|300px|right|Silurian (Llandovery) graptolites from southern Scotland. Locality is probabably Dob's Linn, Moffatdale. 1:50 k sheet 16E (Ettrick), NT 196 158. P772042]]</ins>The well-exposed, virtually continuous Caradoc to Llandovery sequence of graptolite-bearing strata, with its intercalated 'barren beds' was distinguished in the classic researches of Charles Lapworth (1878)<ref>Lapworth, C. 1878. <ins style="font-weight: bold; text-decoration: none;"> </ins>The Moffat Series. Quart. J. Geol. Soc. Lond. 34, 240-346. Lapworth, C. and Wilson, J.1870. The Lower Silurian rocks in the neighbourhood of Galashiels. Trans. Edinb. Geol. Soc. 2, 46-48.</ref> as 'the only section of the Moffat Series which allows us to determine with certainty the sequence and palaeontological characteristics of its component beds, and at the same time exhibits the relationship of the group as a whole to the surrounding greywackes'. Dob's Linn was named after a Scottish Covenanter, Halbert Dobson, who hid from the English Dragoons in the small cave above the waterfall. It is an easily accessible section and abundantly fossiliferous, though at certain critical exposures the visitor is asked to refrain from hammering. Dob's Linn has been the subject of much research (Lapworth 1878<ref>Lapworth, C. 1878. The Moffat Series. Quart. J. Geol. Soc. Lond. 34, 240-346.</ref>, 1970<ref>Toghill, P. 1970. Highest Ordovician (Hartfell Shales) graptolite faunas from the Moffat area, south Scotland. Bull. Br. Mus. Nat. Hist. (Geol.) 19, 1-26.</ref>, Williams 1982-88)(see list in Bibliography below) and is now renowned as the global boundary stratotype for the Ordovician/Silurian boundary (Williams & Ingham 1989)<ref>Williams, S.H. and Ingham, J.K. 1989. The Ordovician-Silurian Boundary Stratotype at Dob's Linn, southern Scotland. In Holland, C.H. and Bassett, M.G. (Editors). A Global Standard for the Silurian System, Nat. Mus. Wales, Geol. Ser. 9, 27-35.</ref>. This lies within a black shale sequence (the Moffat Shale Group) extending from the peltifer graptolite zone of the early Caradoc(Ordovician) to the maximus subzone of the late Llandovery (Silurian). Interbedded volcanic ash horizons are common; Merriman and Roberts (1990)<ref>Merriman, R.J. and Roberts, B. 1990. Metabentonites in the Moffat Shale Group; Southern Uplands of Scotland; geochemical evidence of ensialic marginal basin volcanism. Geol. Mag. 127, 259-271.</ref> describe 135 metabentonite beds cumulating to about 6 m and representing up to 20% of the strata in some biozones (Figure 41). Following Lapworth the Moffat Shale Group is divided into four units with informal formation status: in ascending stratigraphic order these are the Glenkiln Shales, the Lower Hartfell Shales and Upper Hartfell Shales and the Birkhill Shales. The latter are abruptly but conformably overlain by greywackes of the Gala Group, locally assigned to the Queensbury Formation.</div></td></tr>
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</table>JenniferFindlay1https://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=23188&oldid=prevScotfot at 22:23, 6 November 20152015-11-06T22:23:47Z<p></p>
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<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>'''By E.N.K. Clarkson and C.M. Taylor. From Scottish Borders geology: an excursion guide edited by A.D. McAdam, E.N.K. Clarkson, P. Stone. Edinburgh : Scottish Academic Press (for [https://www.edinburghgeolsoc.org/ Edinburgh Geological Society]), 1992.''' </div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>'''By E.N.K. Clarkson and C.M. Taylor. From <ins style="font-weight: bold; text-decoration: none;">[[</ins>Scottish Borders geology: an excursion guide<ins style="font-weight: bold; text-decoration: none;">]] </ins>edited by A.D. McAdam, E.N.K. Clarkson, P. Stone. Edinburgh : Scottish Academic Press (for [https://www.edinburghgeolsoc.org/ Edinburgh Geological Society]), 1992.''' </div></td></tr>
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</table>Scotfothttps://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=7827&oldid=prevScotfot: /* 9. cyphus zone of the Birkhill Shales */2015-03-14T21:45:44Z<p><span dir="auto"><span class="autocomment">9. cyphus zone of the Birkhill Shales</span></span></p>
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<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>An energetic scramble up the Long Burn eventually gains a small waterfall some 3 m high (locality 9). Here is exposed a greywacke horizon, the first known in the sequence, lying within the ''cyphus'' zone of the Birkhill Shales (Rushton & Stone 1991); it can actually be traced some distance along the burn southwards. Above it, just south of the waterfall, are exposed shales of the cyphus and gregarius zones; they are highly fossiliferous and this is one of the best locations for seeing strata from these lower zones of the Silurian in an undisturbed state. Note, too, the soft pale metabentonites characteristic of this part of the sequence.</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>An energetic scramble up the Long Burn eventually gains a small waterfall some 3 m high (locality 9). Here is exposed a greywacke horizon, the first known in the sequence, lying within the ''cyphus'' zone of the Birkhill Shales (Rushton & Stone 1991)<ins style="font-weight: bold; text-decoration: none;"><ref>Rushton, A.W.A. and Stone, P. 1992. Terrigenous input to the Moffat Shale sequence, Southern Uplands of Scotland. Scott. Geol. 27, 167-170.</ref></ins>; it can actually be traced some distance along the burn southwards. Above it, just south of the waterfall, are exposed shales of the cyphus and gregarius zones; they are highly fossiliferous and this is one of the best locations for seeing strata from these lower zones of the Silurian in an undisturbed state. Note, too, the soft pale metabentonites characteristic of this part of the sequence.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[File:MetabentoniteDobsLinn.jpg|300px|thumbnail|Biostratigraphical distribution of metabentonite horizons at Dob's Linn and amounts and proportion of metabentonite in graptolitic zones.]]</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[File:MetabentoniteDobsLinn.jpg|300px|thumbnail|Biostratigraphical distribution of metabentonite horizons at Dob's Linn and amounts and proportion of metabentonite in graptolitic zones.]]</div></td></tr>
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</table>Scotfothttps://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=7826&oldid=prevScotfot: /* 11. vesieulosus and gregarius (triangulatus) zones */2015-03-14T21:44:54Z<p><span dir="auto"><span class="autocomment">11. vesieulosus and gregarius (triangulatus) zones</span></span></p>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 11. ''vesieulosus'' and ''gregarius'' (''triangulatus'') zones ====</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 11. ''vesieulosus'' and ''gregarius'' (''triangulatus'') zones ====</div></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>On moving into the Corrie, strata from two further zones may be examined on the eastern wall, the bedding is now overturned by hill creep. These are the flaggy beds of the ''vesieulosus'' zone, and the hard blocky shales of the ''gregarius'' ''(triangulatus)'' zone in which abundant and finely preserved ''Rastrites peregrinus'' are found. The thin shale bands with numerous interbedded bentonites may be followed right up to the top of the Corrie. Bentonites are especially abundant in the Birkhill Shales and represent successive episodes of volcanic ash-fall which, at least in some instances, have been correlated with successive episodes of graptolite extinction (Batchelor & Weir 1988). Shales of the ''sedgwickii'' zone are exposed in the floor of the Corrie and form a flat plane along its western wall. This zone, however, is better exposed on the south face of the Linn Branch. </div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>On moving into the Corrie, strata from two further zones may be examined on the eastern wall, the bedding is now overturned by hill creep. These are the flaggy beds of the ''vesieulosus'' zone, and the hard blocky shales of the ''gregarius'' ''(triangulatus)'' zone in which abundant and finely preserved ''Rastrites peregrinus'' are found. The thin shale bands with numerous interbedded bentonites may be followed right up to the top of the Corrie. Bentonites are especially abundant in the Birkhill Shales and represent successive episodes of volcanic ash-fall which, at least in some instances, have been correlated with successive episodes of graptolite extinction (Batchelor & Weir 1988)<ins style="font-weight: bold; text-decoration: none;"><ref>Batchelor, R. and Weir, J.A. 1988. Metabentonite geochemistry: magmatic cycles and graptolite extinctions at Dob's Linn, southern Scotland. Trans. R. Soc. Edinb: Earth Sci. 79, 19-41.</ref></ins>. Shales of the ''sedgwickii'' zone are exposed in the floor of the Corrie and form a flat plane along its western wall. This zone, however, is better exposed on the south face of the Linn Branch.</div></td></tr>
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</table>Scotfothttps://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=7825&oldid=prevScotfot: /* 7. Top clingani zone */2015-03-14T21:43:31Z<p><span dir="auto"><span class="autocomment">7. Top clingani zone</span></span></p>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 7. Top ''clingani'' zone ====</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 7. Top ''clingani'' zone ====</div></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>It is possible to climb out, though with care, to this locality, a trench dug in the late 1970s by Henry Williams. He collected in meticulous detail through the top ''clingani'' zone and the full extent of the ''linearis'' zone to establish the order of succession of graptolite faunas as firmly as possible (Williams, 1982).</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>It is possible to climb out, though with care, to this locality, a trench dug in the late 1970s by Henry Williams. He collected in meticulous detail through the top ''clingani'' zone and the full extent of the ''linearis'' zone to establish the order of succession of graptolite faunas as firmly as possible (Williams, 1982)<ins style="font-weight: bold; text-decoration: none;"><ref>Williams, S.H. 1982. Upper Ordovician graptolites from the top Lower Hartfell Shale Formation (D. clingani and P. linearis zones) near Moffat, southern Scotland. Trans. R. Soc. Edinb: Earth Sci. 72, 229-255.</ref></ins>.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[File:AncepsBandsInLinnBranch.jpg|400px|thumbnail|The anceps bands and Ordovician/Silurian boundary stratotype in Linn Branch tranch (modified after Williams 1983).]]</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[File:AncepsBandsInLinnBranch.jpg|400px|thumbnail|The anceps bands and Ordovician/Silurian boundary stratotype in Linn Branch tranch (modified after Williams 1983).]]</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
</table>Scotfothttps://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=7824&oldid=prevScotfot: /* 10. Lower to Upper (Barren) Hartfell Shales */2015-03-14T21:42:05Z<p><span dir="auto"><span class="autocomment">10. Lower to Upper (Barren) Hartfell Shales</span></span></p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 21:42, 14 March 2015</td>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Return to the junction of the Long Burn and the Linn Branch and now proceed westwards via a rough footpath above the Linn Branch, towards the waterfall and locality 10. The succession in the north face of the Linn Branch is near vertical to slightly overturned, younging is constant towards the west and this traverse first passes from Lower to Upper (Barren) Hartfell Shales. Further west a conspicuous eroded gully marks the line of the West Fault which downthrows to the north. Downthrow on this fault causes the aneeps zone at the top of the Ordovician to crop out at the level of the footpath, and the next few metres expose the critical Ordovician/Silurian boundary stratotype section. </div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Return to the junction of the Long Burn and the Linn Branch and now proceed westwards via a rough footpath above the Linn Branch, towards the waterfall and locality 10. The succession in the north face of the Linn Branch is near vertical to slightly overturned, younging is constant towards the west and this traverse first passes from Lower to Upper (Barren) Hartfell Shales. Further west a conspicuous eroded gully marks the line of the West Fault which downthrows to the north. Downthrow on this fault causes the aneeps zone at the top of the Ordovician to crop out at the level of the footpath, and the next few metres expose the critical Ordovician/Silurian boundary stratotype section. </div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>This section, which spans strata containing evidence of a major extinction episode, was carefully excavated and documented by Henry Williams; his paper of 1988 <del style="font-weight: bold; text-decoration: none;">(from which figure40 was taken) </del>records the succession in great detail. The five ''anceps'' bands are clearly shown, highly inclined in the eastern part of the trench within the upper part of the Barren Mudstone sequence. The fauna in these bands is remarkably rich, up to 18 species, including ''Dicellograptus anceps'', having being recorded. The thin ''extraordinarius'' band lies a metre higher than the top ''anceps'' band in the succession (and just above a nodula rlimestone which contains rare blind dalmanitid trilobites). Only three diplograptid species occur in the ''extraordinarius'' band, a dramatic drop from the rich fauna of the ''anceps'' bands. After a further metre of barren beds, black shales resume with abundant graptolites of the uppermost Ordovician ''perseulptus'' zone, and the Ordovician/Silurian boundary is taken at the base of the succeeding ''aeuminatus'' zone. </div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>This section, which spans strata containing evidence of a major extinction episode, was carefully excavated and documented by Henry Williams; his paper of 1988 records the succession in great detail. The five ''anceps'' bands are clearly shown, highly inclined in the eastern part of the trench within the upper part of the Barren Mudstone sequence. The fauna in these bands is remarkably rich, up to 18 species, including ''Dicellograptus anceps'', having being recorded. The thin ''extraordinarius'' band lies a metre higher than the top ''anceps'' band in the succession (and just above a nodula rlimestone which contains rare blind dalmanitid trilobites). Only three diplograptid species occur in the ''extraordinarius'' band, a dramatic drop from the rich fauna of the ''anceps'' bands. After a further metre of barren beds, black shales resume with abundant graptolites of the uppermost Ordovician ''perseulptus'' zone, and the Ordovician/Silurian boundary is taken at the base of the succeeding ''aeuminatus'' zone.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 11. ''vesieulosus'' and ''gregarius'' (''triangulatus'') zones ====</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 11. ''vesieulosus'' and ''gregarius'' (''triangulatus'') zones ====</div></td></tr>
</table>Scotfothttps://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=7823&oldid=prevScotfot at 21:40, 14 March 20152015-03-14T21:40:53Z<p></p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">← Older revision</td>
<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 21:40, 14 March 2015</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l137">Line 137:</td>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>much higher in the slope, which may be reached by direct ascent and via a narrow defile through which the tributary emerges. The depression is floored by masses of loose shale and is probably the best collecting ground for the graptolites of the ''clingani'' zone. The somewhat folded shale is exposed in situ in the walls of the depression.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>much higher in the slope, which may be reached by direct ascent and via a narrow defile through which the tributary emerges. The depression is floored by masses of loose shale and is probably the best collecting ground for the graptolites of the ''clingani'' zone. The somewhat folded shale is exposed in situ in the walls of the depression.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>==== 7. Top clingani zone ====</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>==== 7. Top <ins style="font-weight: bold; text-decoration: none;">''</ins>clingani<ins style="font-weight: bold; text-decoration: none;">'' </ins>zone ====</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It is possible to climb out, though with care, to this locality, a trench dug in the late 1970s by Henry Williams. He collected in meticulous detail through the top ''clingani'' zone and the full extent of the ''linearis'' zone to establish the order of succession of graptolite faunas as firmly as possible (Williams, 1982).</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It is possible to climb out, though with care, to this locality, a trench dug in the late 1970s by Henry Williams. He collected in meticulous detail through the top ''clingani'' zone and the full extent of the ''linearis'' zone to establish the order of succession of graptolite faunas as firmly as possible (Williams, 1982).</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[File:AncepsBandsInLinnBranch.jpg|400px|thumbnail|The anceps bands and Ordovician/Silurian boundary stratotype in Linn Branch tranch (modified after Williams 1983).]]</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[File:AncepsBandsInLinnBranch.jpg|400px|thumbnail|The anceps bands and Ordovician/Silurian boundary stratotype in Linn Branch tranch (modified after Williams 1983).]]</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>==== 8. anceps bands ====</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>==== 8. <ins style="font-weight: bold; text-decoration: none;">''</ins>anceps<ins style="font-weight: bold; text-decoration: none;">'' </ins>bands ====</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Descending to the Long Burn once more one may see a further exposure of the ''anceps'' bands just east of the Main Fault in a second trench cut by Williams and Ingham. Here the succession is, remarkably, about twice the thickness seen in localities to the west of the Main Fault. This is one reason for believing that the Main Fault is a major tectonic thrust which has juxtaposed rock units which may have originally been deposited a long distance away from each other. The ''anceps'' zone faunas are here both abundant and well preserved. </div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Descending to the Long Burn once more one may see a further exposure of the ''anceps'' bands just east of the Main Fault in a second trench cut by Williams and Ingham. Here the succession is, remarkably, about twice the thickness seen in localities to the west of the Main Fault. This is one reason for believing that the Main Fault is a major tectonic thrust which has juxtaposed rock units which may have originally been deposited a long distance away from each other. The ''anceps'' zone faunas are here both abundant and well preserved. </div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>==== 9. cyphus zone of the Birkhill Shales ====</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>==== 9. <ins style="font-weight: bold; text-decoration: none;">''</ins>cyphus<ins style="font-weight: bold; text-decoration: none;">'' </ins>zone of the Birkhill Shales ====</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An energetic scramble up the Long Burn eventually gains a small waterfall some 3 m high (locality 9). Here is exposed a greywacke horizon, the first known in the sequence, lying within the ''cyphus'' zone of the Birkhill Shales (Rushton & Stone 1991); it can actually be traced some distance along the burn southwards. Above it, just south of the waterfall, are exposed shales of the cyphus and gregarius zones; they are highly fossiliferous and this is one of the best locations for seeing strata from these lower zones of the Silurian in an undisturbed state. Note, too, the soft pale metabentonites characteristic of this part of the sequence.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>An energetic scramble up the Long Burn eventually gains a small waterfall some 3 m high (locality 9). Here is exposed a greywacke horizon, the first known in the sequence, lying within the ''cyphus'' zone of the Birkhill Shales (Rushton & Stone 1991); it can actually be traced some distance along the burn southwards. Above it, just south of the waterfall, are exposed shales of the cyphus and gregarius zones; they are highly fossiliferous and this is one of the best locations for seeing strata from these lower zones of the Silurian in an undisturbed state. Note, too, the soft pale metabentonites characteristic of this part of the sequence.</div></td></tr>
<tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l154">Line 154:</td>
<td colspan="2" class="diff-lineno">Line 154:</td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>This section, which spans strata containing evidence of a major extinction episode, was carefully excavated and documented by Henry Williams; his paper of 1988 (from which figure40 was taken) records the succession in great detail. The five ''anceps'' bands are clearly shown, highly inclined in the eastern part of the trench within the upper part of the Barren Mudstone sequence. The fauna in these bands is remarkably rich, up to 18 species, including ''Dicellograptus anceps'', having being recorded. The thin ''extraordinarius'' band lies a metre higher than the top ''anceps'' band in the succession (and just above a nodula rlimestone which contains rare blind dalmanitid trilobites). Only three diplograptid species occur in the ''extraordinarius'' band, a dramatic drop from the rich fauna of the ''anceps'' bands. After a further metre of barren beds, black shales resume with abundant graptolites of the uppermost Ordovician ''perseulptus'' zone, and the Ordovician/Silurian boundary is taken at the base of the succeeding ''aeuminatus'' zone. </div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>This section, which spans strata containing evidence of a major extinction episode, was carefully excavated and documented by Henry Williams; his paper of 1988 (from which figure40 was taken) records the succession in great detail. The five ''anceps'' bands are clearly shown, highly inclined in the eastern part of the trench within the upper part of the Barren Mudstone sequence. The fauna in these bands is remarkably rich, up to 18 species, including ''Dicellograptus anceps'', having being recorded. The thin ''extraordinarius'' band lies a metre higher than the top ''anceps'' band in the succession (and just above a nodula rlimestone which contains rare blind dalmanitid trilobites). Only three diplograptid species occur in the ''extraordinarius'' band, a dramatic drop from the rich fauna of the ''anceps'' bands. After a further metre of barren beds, black shales resume with abundant graptolites of the uppermost Ordovician ''perseulptus'' zone, and the Ordovician/Silurian boundary is taken at the base of the succeeding ''aeuminatus'' zone. </div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>==== 11. vesieulosus and gregarius (triangulatus) zones ====</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>==== 11. <ins style="font-weight: bold; text-decoration: none;">''</ins>vesieulosus<ins style="font-weight: bold; text-decoration: none;">'' </ins>and <ins style="font-weight: bold; text-decoration: none;">''</ins>gregarius<ins style="font-weight: bold; text-decoration: none;">'' </ins>(<ins style="font-weight: bold; text-decoration: none;">''</ins>triangulatus<ins style="font-weight: bold; text-decoration: none;">''</ins>) zones ====</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>On moving into the Corrie, strata from two further zones may be examined on the eastern wall, the bedding is now overturned by hill creep. These are the flaggy beds of the ''vesieulosus'' zone, and the hard blocky shales of the ''gregarius'' ''(triangulatus)'' zone in which abundant and finely preserved ''Rastrites peregrinus'' are found. The thin shale bands with numerous interbedded bentonites may be followed right up to the top of the Corrie. Bentonites are especially abundant in the Birkhill Shales and represent successive episodes of volcanic ash-fall which, at least in some instances, have been correlated with successive episodes of graptolite extinction (Batchelor & Weir 1988). Shales of the ''sedgwickii'' zone are exposed in the floor of the Corrie and form a flat plane along its western wall. This zone, however, is better exposed on the south face of the Linn Branch. </div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>On moving into the Corrie, strata from two further zones may be examined on the eastern wall, the bedding is now overturned by hill creep. These are the flaggy beds of the ''vesieulosus'' zone, and the hard blocky shales of the ''gregarius'' ''(triangulatus)'' zone in which abundant and finely preserved ''Rastrites peregrinus'' are found. The thin shale bands with numerous interbedded bentonites may be followed right up to the top of the Corrie. Bentonites are especially abundant in the Birkhill Shales and represent successive episodes of volcanic ash-fall which, at least in some instances, have been correlated with successive episodes of graptolite extinction (Batchelor & Weir 1988). Shales of the ''sedgwickii'' zone are exposed in the floor of the Corrie and form a flat plane along its western wall. This zone, however, is better exposed on the south face of the Linn Branch. </div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
</table>Scotfothttps://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=7822&oldid=prevScotfot at 21:39, 14 March 20152015-03-14T21:39:17Z<p></p>
<table style="background-color: #fff; color: #202122;" data-mw="interface">
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 21:39, 14 March 2015</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l8">Line 8:</td>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>=== Introduction ===</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>=== Introduction ===</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Some 19 km north-east of Moffat lies Dob's Linn, a spectacular gorge and waterfall deeply cut into the Ordovician and Silurian shales and greywackes of the Southern Uplands. The well-exposed, virtually continuous Caradoc to Llandovery sequence of graptolite-bearing strata, with its intercalated 'barren beds' was distinguished in the classic researches of Charles Lapworth (1878)<ref>Lapworth, C. 1878. The Moffat Series. Quart. J. Geol. Soc. Lond. 34, 240-346. Lapworth, C. and Wilson, J.1870. The Lower Silurian rocks in the neighbourhood of Galashiels. Trans. Edinb. Geol. Soc. 2, 46-48.</ref> as 'the only section of the Moffat Series which allows us to determine with certainty the sequence and palaeontological characteristics of its component beds, and at the same time exhibits the relationship of the group as a whole to the surrounding greywackes'. Dob's Linn was named after a Scottish Covenanter, Halbert Dobson, who hid from the English Dragoons in the small cave above the waterfall. It is an easily accessible section and abundantly fossiliferous, though at certain critical exposures the visitor is asked to refrain from hammering. Dob's Linn has been the subject of much research (Lapworth 1878<ref>Lapworth, C. 1878. The Moffat Series. Quart. J. Geol. Soc. Lond. 34, 240-346.</ref>, 1970<ref>Toghill, P. 1970. Highest Ordovician (Hartfell Shales) graptolite faunas from the Moffat area, south Scotland. Bull. Br. Mus. Nat. Hist. (Geol.) 19, 1-26.</ref>, Williams 1982-88)(see list in Bibliography below) and is now renowned as the global boundary stratotype for the Ordovician/Silurian boundary (Williams & Ingham 1989)<ref>Williams, S.H. and Ingham, J.K. 1989. The Ordovician-Silurian Boundary Stratotype at Dob's Linn, southern Scotland. In Holland, C.H. and Bassett, M.G. (Editors). A Global Standard for the Silurian System, Nat. Mus. Wales, Geol. Ser. 9, 27-35.</ref>. This lies within a black shale sequence (the Moffat Shale Group) extending from the peltifer graptolite zone of the early Caradoc(Ordovician) to the maximus subzone of the late Llandovery (Silurian). Interbedded volcanic ash horizons are common; Merriman and Roberts (1990)<ref>Merriman, R.J. and Roberts, B. 1990. Metabentonites in the Moffat Shale Group; Southern Uplands of Scotland; geochemical evidence of ensialic marginal basin volcanism. Geol. Mag. 127, 259-271.</ref> describe 135 metabentonite beds cumulating to about 6 m and representing up to 20% of the strata in some biozones (Figure 41). Following Lapworth the Moffat Shale Group is divided into four units with informal formation status: in ascending stratigraphic order these are the Glenkiln Shales, the Lower Hartfell Shales and Upper Hartfell Shales and the Birkhill Shales. The latter are abruptly but conformably overlain by greywackes of the Gala Group, locally assigned to the Queensbury Formation.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Some 19 km north-east of Moffat lies Dob's Linn, a spectacular gorge and waterfall deeply cut into the Ordovician and Silurian shales and greywackes of the Southern Uplands. The well-exposed, virtually continuous Caradoc to Llandovery sequence of graptolite-bearing strata, with its intercalated 'barren beds' was distinguished in the classic researches of Charles Lapworth (1878)<ref>Lapworth, C. 1878. The Moffat Series. Quart. J. Geol. Soc. Lond. 34, 240-346. Lapworth, C. and Wilson, J.1870. The Lower Silurian rocks in the neighbourhood of Galashiels. Trans. Edinb. Geol. Soc. 2, 46-48.</ref> as 'the only section of the Moffat Series which allows us to determine with certainty the sequence and palaeontological characteristics of its component beds, and at the same time exhibits the relationship of the group as a whole to the surrounding greywackes'. Dob's Linn was named after a Scottish Covenanter, Halbert Dobson, who hid from the English Dragoons in the small cave above the waterfall. It is an easily accessible section and abundantly fossiliferous, though at certain critical exposures the visitor is asked to refrain from hammering. Dob's Linn has been the subject of much research (Lapworth 1878<ref>Lapworth, C. 1878. The Moffat Series. Quart. J. Geol. Soc. Lond. 34, 240-346.</ref>, 1970<ref>Toghill, P. 1970. Highest Ordovician (Hartfell Shales) graptolite faunas from the Moffat area, south Scotland. Bull. Br. Mus. Nat. Hist. (Geol.) 19, 1-26.</ref>, Williams 1982-88)(see list in Bibliography below) and is now renowned as the global boundary stratotype for the Ordovician/Silurian boundary (Williams & Ingham 1989)<ref>Williams, S.H. and Ingham, J.K. 1989. The Ordovician-Silurian Boundary Stratotype at Dob's Linn, southern Scotland. In Holland, C.H. and Bassett, M.G. (Editors). A Global Standard for the Silurian System, Nat. Mus. Wales, Geol. Ser. 9, 27-35.</ref>. This lies within a black shale sequence (the Moffat Shale Group) extending from the peltifer graptolite zone of the early Caradoc(Ordovician) to the maximus subzone of the late Llandovery (Silurian). Interbedded volcanic ash horizons are common; Merriman and Roberts (1990)<ref>Merriman, R.J. and Roberts, B. 1990. Metabentonites in the Moffat Shale Group; Southern Uplands of Scotland; geochemical evidence of ensialic marginal basin volcanism. Geol. Mag. 127, 259-271.</ref> describe 135 metabentonite beds cumulating to about 6 m and representing up to 20% of the strata in some biozones (Figure 41). Following Lapworth the Moffat Shale Group is divided into four units with informal formation status: in ascending stratigraphic order these are the Glenkiln Shales, the Lower Hartfell Shales and Upper Hartfell Shales and the Birkhill Shales. The latter are abruptly but conformably overlain by greywackes of the Gala Group, locally assigned to the Queensbury Formation.</div></td></tr>
<tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">[[File:DobsLinnExcursionMap.jpg|thumbnail|Overhead view of Dob's Linn.]]</ins></div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Dob’s Linn is conveniently adjacent to the A708 Mofat-Selkirk road. An appropriate starting point for a visit is the watershed some 5 km south-west from the Loch of the Lowes and St. Mary’s Loch. Here on the wall of Birkhill Cottage (NT 202 158) is a plcque erected by Scottish geologists in 1930 commemorating Lapworth’s residence therein at various times during 1872 and 1878, and his discovery of the uses of graptolites in unravelling the stratigraphy and structure of the Southeren Uplands. Some 700 m. west of the cottage are two parking spaces on the north side of the road and conveniently situated for leaving cars or coaches prior to the descent into the Linn. Follow the streamlet from the parking space down to the main burn. Crossing the burn is normally very easy though it can be hazardous after heavy rain.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Dob’s Linn is conveniently adjacent to the A708 Mofat-Selkirk road. An appropriate starting point for a visit is the watershed some 5 km south-west from the Loch of the Lowes and St. Mary’s Loch. Here on the wall of Birkhill Cottage (NT 202 158) is a plcque erected by Scottish geologists in 1930 commemorating Lapworth’s residence therein at various times during 1872 and 1878, and his discovery of the uses of graptolites in unravelling the stratigraphy and structure of the Southeren Uplands. Some 700 m. west of the cottage are two parking spaces on the north side of the road and conveniently situated for leaving cars or coaches prior to the descent into the Linn. Follow the streamlet from the parking space down to the main burn. Crossing the burn is normally very easy though it can be hazardous after heavy rain.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The floor of the valley follows the line of a major fault (the Main Fault of Lapworth). It is still worth noting that to the east of this line the rocks (Birkhill shales) are intensely crushed and folded, and little of stratigraphical value can be determined. All the instructive exposures lie to the west of the fault, the total sequence there is summarized below in descending order. The common graptolites in each zone are indicated, some are illustrated.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The floor of the valley follows the line of a major fault (the Main Fault of Lapworth). It is still worth noting that to the east of this line the rocks (Birkhill shales) are intensely crushed and folded, and little of stratigraphical value can be determined. All the instructive exposures lie to the west of the fault, the total sequence there is summarized below in descending order. The common graptolites in each zone are indicated, some are illustrated.</div></td></tr>
<tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">[[File:DobsLinnGeologicalColumn.jpg|thumbnail|Geological column, timescale after Harland (1989).]]</ins></div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>=== Gala Group (Queensberry Formation) ===</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>=== Gala Group (Queensberry Formation) ===</div></td></tr>
</table>Scotfothttps://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=7819&oldid=prevScotfot at 19:26, 14 March 20152015-03-14T19:26:15Z<p></p>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 15. Hartfell and Birkhill Shales ====</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 15. Hartfell and Birkhill Shales ====</div></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Then proceed west and south crossing the stream above the waterfall, and descending eastwards to the flat platform above the south face of the Linn Branch where the spectacular panorama of the north bank of the Linn Branch can be compared with <del style="font-weight: bold; text-decoration: none;">Figure 42</del>. Note the overturned succession of the Hartfell and Birkhill Shales, Williams' two excavations, the West Fault, and several thrusts in the shales and the greywackes. From the corner just above the north end of the Main Cliff good specimens of ''Cephalograptus corneta'' may be found in the ''convolutus'' zone. Descend from this point to valley floor, either down the scree slope or along the top of the Main Cliff, and thence return to the road. </div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">[[File:NorthCliffDobsLinn.jpg|400px|thumbnail|Panoramic view of North Cliff from locality 15.]]</ins></div></td></tr>
<tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Then proceed west and south crossing the stream above the waterfall, and descending eastwards to the flat platform above the south face of the Linn Branch where the spectacular panorama of the north bank of the Linn Branch can be compared with <ins style="font-weight: bold; text-decoration: none;">the diagram</ins>. Note the overturned succession of the Hartfell and Birkhill Shales, Williams' two excavations, the West Fault, and several thrusts in the shales and the greywackes. From the corner just above the north end of the Main Cliff good specimens of ''Cephalograptus corneta'' may be found in the ''convolutus'' zone. Descend from this point to valley floor, either down the scree slope or along the top of the Main Cliff, and thence return to the road. </div></td></tr>
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</table>Scotfothttps://earthwise.bgs.ac.uk/index.php?title=Dob%27s_Linn,_Moffat_-_an_excursion&diff=7817&oldid=prevScotfot: /* 7. Top clingani zone */2015-03-14T19:22:53Z<p><span dir="auto"><span class="autocomment">7. Top clingani zone</span></span></p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 19:22, 14 March 2015</td>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 7. Top clingani zone ====</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==== 7. Top clingani zone ====</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It is possible to climb out, though with care, to this locality, a trench dug in the late 1970s by Henry Williams. He collected in meticulous detail through the top ''clingani'' zone and the full extent of the ''linearis'' zone to establish the order of succession of graptolite faunas as firmly as possible (Williams, 1982).</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>It is possible to climb out, though with care, to this locality, a trench dug in the late 1970s by Henry Williams. He collected in meticulous detail through the top ''clingani'' zone and the full extent of the ''linearis'' zone to establish the order of succession of graptolite faunas as firmly as possible (Williams, 1982).</div></td></tr>
<tr><td colspan="2" class="diff-side-deleted"></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">[[File:AncepsBandsInLinnBranch.jpg|400px|thumbnail|The anceps bands and Ordovician/Silurian boundary stratotype in Linn Branch tranch (modified after Williams 1983).]]</ins></div></td></tr>
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