OR/14/063 Site assessment - ELC 10: Dirleton Castle

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Whitbread, K, Ellen, R, Callaghan, E, Gordon, J E, and Arkley, S. 2014. East Lothian geodiversity audit. British Geological Survey Internal Report, OR/14/063.
ELC_10: Dirleton Castle
Site Information
Location and Summary Description:

Dirleton Castle is located within the village of Dirleton and is perched on a porphyritic trachyte crag within the grounds. The igneous rock is part of the Garleton Hills Volcanic Formation and was extruded as lava during the Carboniferous age. The ruined castle dates back to the late 13th Century and underwent three phases of building. Due to its elevated position it was ideal for defensive purposes from land and sea.

National Grid Reference:

Mid-point: 351616, 683954

Site type:
  • Natural exposure
Site ownership: Historic Scotland Current use: * Visitor Attraction
Field surveyors: Sarah Arkley and Eileen Callaghan Current geological designations: None known
Date visited: 14th May 2014 Other designations: Scheduled Ancient Monument, Castle, doocot and boundary wall are Category A listed buildings
Site Map
Figure 15    Dirleton Castle Location Map. The site boundary is drawn to include key exposures, access to the castle and grounds and coincides with the area of the Scheduled Ancient Monument. The castle itself is also considered to be part of the geologically significant area associated with the site.
Site Description
Background

Dirleton Castle lies within the village of Dirleton approximately 2.5 km from the town of North Berwick. The castle stands on an outcrop of porphyritic trachyte, forming part of the Garleton Hills Volcanic Formation (ELC_10 P1). Dirleton Castle is owned by Historic Scotland who charges for entry into the castle and grounds. The castle’s strategic position lends to good views of the surrounding countryside and coast.

Igneous Rocks
The red-purple stained, fine-grained trachyte lava exposed at Dirleton Castle is typical of the trachyte lavas which form the Garleton Hills. The north-west corner of the exposure is up to 5 metres in height displaying large jointed faces (Photo ELC_10 P2). The porphyritic trachyte is purplish in colour, with feldspar phenocrysts up to 5 mm in size, (Photo ELC_10 P3) and weathered out vesicles. The exposure to the west and south is blockier in appearance, (ELC_10 P4), again purplish in colour with vesicles (ELC_10 P5).

Concentric ring structures (ELC_10 P6) are seen within the trachyte at the western edge of the exposure. These structures, exposed by weathering, may be original features which may have developed through cooling of the lavas.

Access and Additional Information
Dirleton Castle is easily accessible as it is owned and managed by Historic Scotland. It is open throughout the year and opening times can be found on their website. There is a charge for entry into the castle and gardens.

The castle is constructed of igneous blocks, probably locally derived and dressed in sandstone that may have been derived from quarries near the nearby village of Gullane (ELC_10 P7).

Stratigraphy and Rock Types
Age: Lower Carboniferous Formation: Garleton Hills Volcanic Formation
Rock type: Porphyritic trachyte
Assessment of Site: Access and Safety
Aspect Description
Road access and parking Located within the village of Dirleton, the castle is easily accessed by car and bus. The A198 passes Dirleton village. There is parking beside the castle and also public toilets.
Safety of access The site is easily accessible with paths throughout the site.
Safety of exposure Some of the faces exposed are up to 5 metres in height. Where the rock is weathered and fractured care should be taken when observing the exposure close up. There are signs prohibiting climbing on the rocks.
Access Historic Scotland charge an admission fee for entry to the castle and grounds.
Current condition The rock is well exposed and free from vegetation. The surfaces are weathered but on close inspection fractures, structural features and composition of the rock can be seen.
Current conflicting activities Tourist attraction.
Restricting conditions Opening times of the site.
Nature of exposure Natural exposure.
Assessment of Site: Culture, Heritage & Economic Value
Aspect Description
Historic, archaeological & literary associations Dirleton Castle dates back to the 13th Century and has been partially destroyed, rebuilt and extended over the following 400 years (ELC10_P8). The gardens that surround the castle date from the late 19th and early 20th centuries. The Nisbet family passed the castle and gardens into state care in the 1920’s.
Aesthetic landscape Historic building sited on a natural exposure of rock.
History of Earth Sciences John Muir Way passes through Dirleton.
Economic geology The castle building stone may have been brought from Gullane Quarry.
Assessment of Site: GeoScientific Merit
Rarity Quality Literature/Collections Primary Interest
Lithostratigraphy
Sedimentology
Igneous/Mineral/Metamorphic Geology Local Excellent X
Structural Geology
Palaeontology
Geomorphology
Site Geoscientific Value

The rock on which Dirleton Castle is situated is an excellent exposure of porphyritic trachyte of the Garleton Hills Volcanic Formation. The rock is well exposed, free from vegetation and easily accessible. The castle and grounds are managed by Historic Scotland which charge entry into the site.
Dirleton Castle and crag provides an excellent example of Carboniferous extrusive volcanic rock, with local significance. The overall site has important historical associations.

Assessment of Site: Current site usage
Community The site is visited throughout the year; figures show it had 24 512 visitors in 2013–14 (figures from the Historic Scotland website).
Education The site at present is probably used for historical relevance rather than earth science education.
Assessment of Site: Fragility and potential use of the site
Fragility Weathering; activities relating to heritage preservation that may obscure the rock features.
Potential use On site interpretation. At present there are interpretation boards with relation to the history of the castle (ELC_10 P8), a paragraph of the rock outcrop could be added to these. The John Muir Way passes through Dirleton, information pertaining to the outcrop could be added to their literature or an interpretation board could be erected on the village green.
Geodiversity Summary
The main value of this site is the historical association that Dirleton Castle has within East Lothian. There are other exposures of porphyritic trachyte at nearby Craigs Quarry (ELC_11), Peppercraig Quarry (ELC_3) in Haddington, and Yellowcraig Coast (ELC_6). The exposure at Dirleton Castle provides one of the best exposures of porphyritic trachyte across East Lothian, with direct historical associations.


Site Photos
Photo ELC_10 P1:    View of Dirleton Castle, built upon a crag of porphyritic trachyte. © BGS, NERC.
Photo ELC_10 P2:    Good exposure of the trachyte is found within crags at the north-west corner of the site. © BGS, NERC.
Photo ELC_10 P3:    Feldspar phenocrysts within the trachyte, measuring up to 5 mm in size. © BGS, NERC.
Photo ELC_10 P4:    The trachyte is more blocky in appearance to the south and west of the site.
© BGS, NERC.
Photo ELC_10 P5:    Weathered out feldspars and vesicles (formed by gas bubbles within the laval) give the trachyte a pockmarked appearance in places. © BGS, NERC.
Photo ELC_10 P6:    Structural features within the trachyte, such as these concentric rings, are exposed through weathering. It is thought these ellipsoids were developed during the cooling process of the lava.
© BGS, NERC.
Photo ELC_10 P7:    Blocks of igneous rock (dark reddish brown) have been used in the construction of the castle; the castle has then been dressed by the paler yellow/white sandstone blocks which are seen weathering in the photograph. © BGS, NERC.
Photo ELC_10 P8:    Existing Interpretation panel describing the history of Dirleton Castle. Additional information could be provided on interpretation boards like these to describe the bedrock foundations on which the castle is built. © BGS, NERC.