Ard Hill
Geological Conservation Review site | GCR #842 | Structural and Metamorphic Geology | Moine
Scotland's geosites are chosen because of their local, national or international importance. Take only photos, leave only footprints: avoid causing any damage to this site. You can walk almost anywhere in Scotland without the need to ask permission or keep to paths, but you have a responsibility to care for your own safety, to respect people's privacy and peace of mind and to cause no damage.
This site is a Site of Special Scientific Interest (SSSI). It is an offence to intentionally or recklessly damage the protected natural features of a SSSI, and this includes unauthorised sample collection.
The right of access does not extend to quarries, building sites or any land where public access is prohibited, or to the collection of geological samples.
Summary
Historically an important location cited in support of the idea that mylonites formed as deformation fabrics distinct from thrust localisation and displacement
This site provides an exceptionally informative section across the Balmacara Thrust Plane and the middle nappe of the Moine Thrust Zone, involving the Torridonian and Lewisian mylonites. Shore exposures reveal deformed Torridonain sandstones, which become more intensely deformed towards the promontory of Ard Hill, approaching the Balmacara Thrust Plane. This thrust lies in unexposed ground in a small bay [NG818263]. Folded, mylonitic, acidic Lewisian crops out on the southern side of this bay. Separating the Torridonian and Lewisian mylonites is a distinct zone of brecciation, indicating that some thrust movements occurred after mylonitisation. Ard Hill was once thought to provide a key site within the Thrust Belt to demonstrate the important distinction in time between mylonitisation and thrusting. This notion is now abandoned in light of more recent research at Eriboll and northern Assynt... thrust displacement and mylonitisation are intimately related... late movements and complex sequencing can create the cataclastic ovderprinting of mylonites preserved at Ard Hill.
Site information
Access
Best visited at low tide.
Cars can be parked in the Ard Hill FLS car park, signposted just east of Reraig.
Daniel Burgess
March 30, 2024
Mylonitic Torridonian sandstone (Sleat Group)
Daniel Burgess
March 30, 2024
Mylonitic Lewisian Gneiss in the hanging wall of the Balmacara Thrust. The dip of the mylonitic foliation has steepened relative to that in the structurally underlying Torridonian.