CITATION AIRD TORRISDALE SITE OF SPECIAL SCIENTIFIC INTEREST () Site code: 24

NATIONAL GRID REFERENCE: NC 676629

OS 1:50,000 SHEET NO: Landranger Series 10 1:25,000 SHEET NO: Explorer Series 448

AREA: 135.10 hectares

NOTIFIED NATURAL FEATURES Geological: Structural and metamorphic geology: Moine

DESCRIPTION Aird Torrisdale Site of Special Scientific Interest (SSSI) is located on the north coast of Sutherland, 3km west of Bettyhill. The site is a nationally important example of Moine geology.

Moine rock was originally sandy sediment deposited on the floor of an ocean over 950 million years ago. This rock underlies much of the north of to the east of Eriboll. The Moine rock, and the Lewisian basement rock on which Moine rock was deposited, were pushed westwards during the Caledonian orogeny (or mountain building event) around 480-420 million years ago. The rocks broke into a series of four sheets or ‘nappes’ separated by ‘thrust zones’ where each westward-moving sheet overrode the sheet in front of it.

The rocks at Aird Torrisdale provide superb exposures across the Naver Thrust Zone, that separates the A’ Mhoine Nappe to the west from the Naver Nappe to the east. This is a major structural boundary within the rocks of northern Scotland. At Aird Torrisdale, the thrust zone includes two major thrust faults: the Naver Thrust that bounds the thrust zone to the southwest, and the Torrisdale Thrust that bounds the thrust zone to the northeast. Both thrusts were ductile (the rocks behaved like soft plastic during fault movement). The Torrisdale Thrust stacked rocks from the Naver Nappe - highly migmatised (partly melted) Moine rocks, and their underlying Lewisian basement rocks - on top of less strongly migmatised Moine and Lewisian rocks. The Naver Thrust stacked these less strongly migmatised rocks on top of non- migmatised (unmelted) Moine and Lewisian rocks of the A’ Mhoine Nappe. Both thrusts are readily seen, making them ideal for study.

NOTIFICATION HISTORY First notified under the 1949 Act: 1963 and 1975 Re-notified under the 2004 Act: 29 June 2012 with a 42.93ha decrease in area

REMARKS Area of site reduced (from 178.03 ha).

A small part of Aird Torrisdale SSSI overlaps a small part of SSSI which is designated for the notified features listed below.

Coastal geomorphology of Scotland Sand dunes Saltmarsh Upland assemblage Vascular plant assemblage