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Pentland Hills

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Pentland Hills

The Pentland Hills are a range of hills southwest of Edinburgh, Scotland. The range is around 20 miles (30 kilometres) in length, covers an area of 35 square miles (91 km2), and runs southwest from Edinburgh towards Biggar and the upper Clydesdale. The hills have been designated as a Scottish regional park.

The hills take their name from the hamlet of Pentland, situated a short distance beyond the eastern end of the range. The hamlet's name, which was first recorded in the 12th century, probably comes from Cumbric pen llan, meaning "head or top end of the church or enclosure". It was applied to the nearby hills from the 16th century onwards. The name of the Pentland Firth, the strait separating Orkney from Caithness, is entirely unrelated.

The southern and western parts of the Pentland Hills are formed from sandstones together with some conglomerates, all of Devonian age and assigned to the Old Red Sandstone. Within the sedimentary sequence are extrusive igneous rocks, principally of basaltic and andesitic composition. The sedimentary rocks are also intruded by dykes of porphyrite.

The oldest rocks are a sequence of Silurian mudstones, siltstones and sandstones collected together as the North Esk Group. From oldest to youngest they comprise the Llandovery age Reservoir Formation (named for North Esk Reservoir where these rocks are to be found), the Deerhope Formation, the Cock Rig Formation and the Wether Law Linn Formation overlain by the Wenlockian age Henshaw Formation. These are in turn unconformably overlain by the late Silurian to early Devonian age sandstones and conglomerates of the Greywacke Conglomerate and Swanshaw Sandstone formations. A further unconformity separates these from the overlying Pentland Hills Volcanic Formation though all three formations are collected together within the Lanark Group. The Volcanic Formation forms such summits as East and West Kip.

The southeastern edge of the range is defined by the Pentland Fault with a substantial downthrow to the southeast. Running NE-SW through the middle of the range is the Cairnmuir Fault which downthrows to the northwest. West Cairn Hill and East Cairn Hill are formed by the sandstones of the Kinnesswood Formation which reach as far north as Hare Hill (though also underlie much of the southeastern part of Edinburgh) and which terminate to the southeast at the Cairnmuir Fault. The Kinnesswood sandstones together with rocks of the Ballaggan Formation, which form the lower ground immediately northwest of the Pentlands, constitute the early Carboniferous age Inverclyde Group.

Black Hill stands out as being an intrusion of microgranite or felsite, as in part is nearby Harbour Hill. South Black Hill on the other hand, together with Scald Hill and Carnethy hill are formed from various lithologies of the Pentland Hills Volcanic Formation, as too are Allermuir, Caerketton and Castlelaw hills. The Volcanic Formation gives rise to generally steeper and craggier hillsides as these rocks are more resistant to erosion than the sedimentary rocks.

Much of the lower ground is covered by glacial till from the last ice age. Glacial meltwater channels are identified in places as at Deer Hope and the deep cleft of Green Cleugh between Hare Hill and Black Hill.

The peaks include:

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