Geology of the Bath area: Pre-Carboniferous rocks - Revision history

Dbk at 13:40, 2 December 2015

2015-12-02T13:40:10Z

← Older revision		Revision as of 14:40, 2 December 2015
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	[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]		[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]

	Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district ('''~~Figure~~ P785914'''). During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly ('''~~Figure~~ P785915'''). To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline''' ('''~~Figure~~ P785914''').		Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district ('''P785914'''). During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly ('''P785915'''). To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline''' ('''P785914''').

	[[Image:P785915.jpg\|thumb\|left\|300px\|Bouguer gravity anomaly map of the Bath district and adjacent areas. P785915.]]		[[Image:P785915.jpg\|thumb\|left\|300px\|Bouguer gravity anomaly map of the Bath district and adjacent areas. P785915.]]

Dbk at 15:36, 28 July 2015

2015-07-28T15:36:20Z

← Older revision		Revision as of 16:36, 28 July 2015
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	<br clear=all>		<br clear=all>
	== Geology of the Bath area - contents ==		== Geology of the Bath area — contents ==
	{{Bathpapges}}		{{Bathpapges}}


	[[Category:Bath - the geology of the area\| 003]]		[[Category:Bath - the geology of the area\| 003]]

Dbk at 14:41, 29 January 2015

2015-01-29T14:41:13Z

← Older revision		Revision as of 15:41, 29 January 2015
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	<references/>		<references/>

			<br clear=all>
	== Geology of the Bath area - contents ==		== Geology of the Bath area - contents ==
	{{Bathpapges}}		{{Bathpapges}}

Dbk at 16:46, 28 January 2015

2015-01-28T16:46:06Z

← Older revision		Revision as of 17:46, 28 January 2015
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	== References ==		== References ==
			<references/>

	~~<references/>~~		== Geology of the Bath area - contents ==
			{{Bathpapges}}


	[[Category:Bath - the geology of the area\| 003]]		[[Category:Bath - the geology of the area\| 003]]

Dbk at 12:41, 7 July 2014

2014-07-07T12:41:40Z

← Older revision		Revision as of 13:41, 7 July 2014
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			__NOTOC__
	{{BathSE}}		{{BathSE}}
	[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]		[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]

Jeth1 at 13:13, 3 July 2014

2014-07-03T13:13:57Z

← Older revision		Revision as of 14:13, 3 July 2014
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	[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]		[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]

	Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district (Figure P785914). During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly (Figure P785915). To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline''' (Figure P785914).		Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district ('''Figure P785914'''). During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly ('''Figure P785915'''). To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline''' ('''Figure P785914''').

	[[Image:P785915.jpg\|thumb\|left\|300px\|Bouguer gravity anomaly map of the Bath district and adjacent areas. P785915.]]		[[Image:P785915.jpg\|thumb\|left\|300px\|Bouguer gravity anomaly map of the Bath district and adjacent areas. P785915.]]

Jeth1 at 13:12, 3 July 2014

2014-07-03T13:12:43Z

← Older revision		Revision as of 14:12, 3 July 2014
Line 2:		Line 2:
	[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]		[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]

	Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district (Figure 1). During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly (Figure 2). To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline''' (Figure 1).		Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district (Figure P785914). During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly (Figure P785915). To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline''' (Figure P785914).

	[[Image:P785915.jpg\|thumb\|left\|300px\|Bouguer gravity anomaly map of the Bath district and adjacent areas. P785915.]]		[[Image:P785915.jpg\|thumb\|left\|300px\|Bouguer gravity anomaly map of the Bath district and adjacent areas. P785915.]]

Jeth1 at 13:09, 3 July 2014

2014-07-03T13:09:54Z

← Older revision		Revision as of 14:09, 3 July 2014
Line 2:		Line 2:
	[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]		[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]

	Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district. During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly. To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline'''.		Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district (Figure 1). During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly (Figure 2). To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline''' (Figure 1).

	[[Image:P785915.jpg\|thumb\|left\|300px\|Bouguer gravity anomaly map of the Bath district and adjacent areas. P785915.]]		[[Image:P785915.jpg\|thumb\|left\|300px\|Bouguer gravity anomaly map of the Bath district and adjacent areas. P785915.]]

Dbk: Protected "Geology of the Bath area: Pre-Carboniferous rocks" ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite)) [cascading]

2014-06-11T12:34:23Z

Protected "Geology of the Bath area: Pre-Carboniferous rocks" ([Edit=Allow only administrators] (indefinite) [Move=Allow only administrators] (indefinite)) [cascading]

← Older revision	Revision as of 13:34, 11 June 2014
(No difference)

Dbk at 09:54, 22 May 2014

2014-05-22T09:54:44Z

← Older revision		Revision as of 10:54, 22 May 2014
Line 1:		Line 1:
	{{BathSE}}		{{BathSE}}
	~~{\| class="wikitable" width="100pt" style="margin-left~~:~~10px; margin-right:0px; margin-bottom:10px; float:right; text-align:left;"~~		[[Image:P785914.jpg\|thumb\|350px\|Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). P785914.]]
	\| ~~<img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=380058&width=379&height=491">~~
	\|-
	\| Generalised pre-Permian subcrop map of the district Sections 1 and 2 are lines of section shown on the published 1:50 000 geological map (Sheet 265, Bath). ~~[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=380058&size=1000~~ P785914].
	\|}

	Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district. During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly. To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline'''.		Little is known of the pre-Devonian succession. Tremadoc strata are known to the north and it is probable that Silurian volcanic rocks are present at depth, connecting the outcrops in the Mendips and at Tortworth. The Hamswell Borehole (ST77SW 1 [7348 7088]) penetrated around 300 m of red-brown mudstone, dipping 15 to 30° and belonging to the Raglan Mudstone Formation (Silurian, Pridoli age). The formation lies in the lower part of the Lower Old Red Sandstone Group, '''Old Red Sandstone Supergroup''', and younger Devonian-age Old Red Sandstone strata are inferred to be present at depth more widely across the district. During the Devonian, the Bath district lay within a broad, low-lying coastal plain on the southern margin of a continent known as Laurussia, bordered to the north by uplands stretching from North Wales to the Pennines and East Midlands, and to the south by an ocean basin. Major (Acadian) uplift in the Mid Devonian created an unconformity between the Lower and Upper Old Red Sandstone groups. On the northern edge of the district, the Upper Old Red Sandstone is exposed at the eastern end of the Chipping Sodbury railway cutting [733 816] (Green, 1992,<ref>Green, G W. 1992. British regional geology: Bristol and Gloucester region. Third edition. (London: HMSO for British Geological Survey.)</ref> fig. 21). Here, about 10 m of '''Tintern Sandstone Formation''' (TS), of latest Devonian (Famennian) age, comprises purplish brown sandstone with subordinate mudstone beds and scattered pebbles. The succession records the gradual change at the end of the Devonian from fluvial sedimentation to marine deposition that was fully established in the early Carboniferous. All these occurrences of Old Red Sandstone are inferred to form the culmination of the ‘Bath Axis’, a westerly-dipping monocline at depth, possibly overlying a Variscan displacement, and forming a basement high of dense rocks that is very apparent as a high gravity anomaly. To the west this axis is bounded by the north–south trending '''Coalpit Heath''' and '''Pensford–Radstock synclines''' and the intervening east–west '''Kingswood Anticline'''.

	{\| ~~class="wikitable" width="100pt" style="margin-~~left~~: 0px; margin-right: auto;"~~		[[Image:P785915.jpg\|thumb\|left\|300px\|Bouguer gravity anomaly map of the Bath district and adjacent areas. P785915.]]
	~~\| <img src="http://bgsintranet/asset-bank/action/directLinkImage?assetId=380059&width=300&height=200">~~
	\|-
	\| Bouguer gravity anomaly map of the Bath district and adjacent areas. ~~[http://bgsintranet/asset-bank/action/viewFullSizedImage?id=380059&size=1000~~ P785915].
	\|}

	== References ==		== References ==