Local Geodiversity Sites are places where the variety of geology of the local area can be enjoyed and appreciated. In December 2022, 19 sites were approved by the Lothian and Borders GeoConservation Committee for Midlothian Council to designate as Local Geodiversity Sites.
The Midlothian district lies south of the A720 Edinburgh Bypass and is bounded to the east by the agricultural lands of East Lothian, to the south by the steep scarp of the Moorfoot Hills and to the west by the dramatic Pentland Hills. Most of the region is drained by the Rivers North and South Esk and their tributaries, which rise in the Pentland and Moorfoot Hills and have eroded deep denes and glens into the landscapes of Midlothian.
The solid geology is varied, consisting of a basin of Carboniferous rocks – the Midlothian coalfield – surrounded by the rugged Pentland hills, which are largely igneous in origin, and the Lower Palaeozoic greywackes that form the gently rounded Moorfoot Hills. Thick sequences of glacial, post-glacial and alluvial deposits were deposited over the lowlands as the ice sheets of the last glacial event melted.
Highlights include the following accessible sites:
Crichton Castle Quarry LGS [NT 3807 6103]
Carboniferous Aberlady Formation pink and cream sandstone extracted from this quarry probably provided building materials for Crichton Castle and outbuildings. Parking is available in the car park by Crichton Kirk [NT 381 616]. Walk south to Crichton Castle and take the left path towards the ruined building, then look on the left for a rough path which climbs up the grassy slope into the sandstone quarry. The quarry floor is largely overgrown with bracken, thistles and gorse and is best visited in winter. The medium to coarse-grained sandstone has bedding-planes with a gentle dip to the north-west and features such as small iron nodules, soft-sediment deformation and cross-bedding.
Currie Lee Quarry, Crichton LGS [NT 3803 6235]
Currie Lee Quarry has extensive exposures of Lower Carboniferous Blackhall Limestone. The access from Vogrie House follows a path upstream on the western bank of the Tyne Water which reaches the north end of the quarry, where a limestone cliff face hangs over a pool.
The quarry extends for about 300 m from the most recently worked face in the north to the earliest workings at the southern end, now largely overgrown. The upper beds consist of horizontal, thinly-bedded, pale grey limestones. At the base of the face throughout the quarry, a massive bed of fossil-rich limestone, at least several metres thick, can be found. At the southern end of the quarry is a limekiln which may be unsafe. The best views are available during the winter months, when foliage does not obscure the limestone faces.
Dalkeith Country Park LGS
The Local Geodiversity Site in the country park covers the glens of the River South Esk from Old Cow Bridge to the Meeting of the Waters [NT 3393 6913] and the River North Esk from Montagu Bridge to the Meeting of the Waters.
Dalkeith lies across the centre of the Midlothian Coalfield syncline and therefore exposures of Midlothian’s youngest rocks, the Carboniferous Upper Coal Measures, can be found in this area. The Rivers South and North Esk have eroded deep glens upstream from their confluence at the Meeting of the Waters. Good exposures of the rocks of the Coal Measures are found along the banks and channels of both rivers, but most of the area between the two rivers is covered by sand and gravel glacial meltwater deposits overlying glacial till.
Habbie’s Howe LGS [NT1691 5640 (south) – NT 1783 5657 (north)]
The River North Esk flows through a steep-sided valley between Amazondean and Craigy Bield in the grounds of Newhall, near Carlops. The rocks consist of limestones, sandstones and mudstones of the Carboniferous Lower Limestone Formation and are exposed in the sides of the valley, in a small waterfall and in a disused quarry at Mill Bridge. The valley was probably formed by the erosion and undercutting of sandstones by glacial meltwater and has been modified by eighteenth century landscaping. The valley is linked to the 1725 pastoral comedy, ‘The Gentle Shepherd’ by Allan Ramsay. There are many footpaths through the woods which are accessible by road and tracks from the public car park in Carlops.
Loganlee Inlier, Pentland Hills LGS NT 1867 6186
The Loganlee Inlier is one of three small areas of rocks of Silurian age in the Pentland Hills. Green Cleugh and the glen of Logan Burn, near the dwelling named The Howe, are steep-sided valleys which expose near-vertical greywackes and mudstones beds containing Silurian fossils, as well as structures which show that the beds are inverted. The greywackes can be seen along a 300 m slope on the north side of the valley and are associated with other rocks, particularly igneous felsites and basaltic tuffs. There are also exposures of Old Red Sandstone conglomerates in Green Cleugh and Logan Burn.
Roslin Glen LGS [NT 2737 6256 (south) to NT 2866 6448 (north)]
Roslin Glen is the most dramatic meltwater gorge in Midlothian and is deeply incised into Carboniferous Passage Formation sandstones which are seen in high cliffs along the length of the glen. The River North Esk erodes into the coarse-grained reddish sandstone beds, which are many metres thick, exposing bedrock that is seen in the river bed in several places and forms small waterfalls. River caves are found in places in the sides of the glen well above present river level and were probably eroded when the gorge was filled with meltwater. To the north and south of the gorge section the valley opens out, although steep cliffs still tower over the alluvial flood plains south of Roslin Castle, as well as between Polton and Hewan Bog.
Roslin Glen South LGS [NT 2683 6267 (gateway) – NT 2652 6209 (weir)]
This section of Roslin Glen is a post-glacial meltwater valley, in which the valley floor is wide enough to house the buildings of the Roslin Glen gunpower works, now disused. Sandstones, mudstones and siltstones of the Carboniferous Upper Limestone Group can be seen between the gateway and the gunpowder works in several small quarries which are obscured in places by soil wash and fallen trees. The 25 m high river cliff on the River North Esk near the mill buildings has an excellent section of the Upper Limestone Group, with siltstones and mudstones at the base and thick beds of sandstone above, seen best through binoculars.