The most striking feature about the topography of Caithness is its flatness. In Scotland, only Buchan rivals the plain of Caithness for its big skies and distant horizons. Given its position on the fringes of the Northern Highlands, the low relief of Caithness requires some explanation.

The plain is partly controlled by rock structure. The low dips of the Devonian flagstones lead to the development of gentle slopes, with thick, hard beds forming ramp-like surfaces. On the main hills, such as Ben-a-chielt, the outline of the hill is stepped and the hilltop is flat, a reflection of glacial erosion of horizontally-bedded flagstones and sandstones of uneven resistance. Glacial erosion has undoubtedly been significant – deepening valleys and streamlining ridges – but its planar integrity remains.

The plain started as a major erosion surface, created by long denudation before the Ice Age. Godard (1965) pointed out that the erosion surface locally, as around Camster, cuts the 5-10º dip of the Devonian. Also, it extends onto the basement rocks. So, it is not a simple structural slope. The termination of the Caithness plain in cliffs at the coast indicates that the plain has been uplifted by around 100 m. Yet the amount of tilting, warping and differential movement has been modest. Godard (1965) regarded the plain as an uplifted surface developed around the fringes of the Highlands during the last 10 million years or so. We don’t know why and when that uplift happened.

Across the Moray Firth, the equivalent low plateau in Buchan carries sediments and deep weathering covers that indicate that the flattening of the terrain started long ago. Buchan was already an area of low relief in the late Mesozoic – it retains traces of Cretaceous flint and greensand – and not greatly affected by the mighty earth movements that threw up the Scottish Highlands around 60 million years ago. Indeed, Buchan and Caithness may have a similar earth histories, given their proximity to the thick Mesozoic rocks on the floor of the Moray Firth. The plain of Caithness may be, in its broadest outlines, a very ancient feature indeed.

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