Image: Oldwick Castle – vertical and steeply-inclined cliffs and deep geos developed on dipping Devonian flagstones. (Adobe Stock / 221601774)

The single most important factor determining cliff form on the hard rock coasts of Caithness is the structure of the rock – the way that the rocks are lying and the orientation and number of fractures. The effects can be seen in both plan view – on the map and from above – and in cross section – moving from sea level to the cliff top.

The simplest structure is that of horizontally-dipping sedimentary rocks. Here the detail of the cliff face is controlled by differential weathering and erosion of the rock beds and produces a series of ledges, notches and caves. The flagstone layers are etched into friezes and the cornices adopted by nesting seabirds. If the cliff is capped by thick till then the slope of the upper till is sharply reduced.

Since both sandstones and flagstones are also extensively cracked and faulted, often in rectangular patterns, the detail of the cliff forms are dominated by blocky shapes, and cut by inlets (geos) and ravines which often bisect headlands. This contributes to the development of an exceptionally rich heritage of caves, arches and stacks.

Where dip or foliation lies to seaward then the cliff face is inherently unstable. Removal or collapse of rock towards the cliff base leads to rock slides. Recent rock slides can often be recognised at the base of these cliffs and the lack of rounding of debris suggest that it is soon removed by the sea.

In plan view, the outline of the coast often shows headlands and geos. The geos can usually be traced to lines of weakness provided by trap dykes, faults and master joints. The headlands, as well as showing relatively low fracture densities, often relate to resistant rocks.

Latheronwheel - vertical cliffs in gently dipping flagstones, with master joints providing slide planes

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