Vol. 1. No. 6. October, 1975.

THE RAISED SHORELINES OF CAITHNESS
D. Omand

Skirting some parts of the coast of Caithness are marine deposits representing beaches now elevated above sea level. Since these beaches were first reported in the literature (Crampton et alia 1914) contrasting views have been expressed on their interpretation as well as on their altitudes above sea level.

1. High Level
Crampton et alia (1914) remarked on the absence of the 30m and 15m raised beaches in Caithness. Agreeing in the main, Charlesworth (1957,Vol.2) found, at the 30m level, "A well-defined beach skirting . . . . the north coast from Durness to Reay", but thought its non-existence in Caithness a mystery that might be explained by tilting or faulting, rapidly changing sea levels, or to ice persisting off the coast, possibly in a stagnant state. Godard argued that vestiges of high late-glacial beaches survive in Caithness at Dunbeath (15m) and at Latheronwheel (17m) above high water mark, but qualified the statement by calling them "slightly doubtful evidences". Their relatively low altitude is explained on the grounds that Caithness, being a peripheral region did not have such a thick blanket of ice pressing down on its surface and so had a lesser isostatic readjustment (Godard 1965). Smith (1968) found "washing limits" - the highest levels at which sea stood upon the land - where re-entrants diversify the cliff coast as at Lybster, Janetstown and at Dunbeath. By contrast, a map of Sissons (1967, P.163, Fig.68) shows the zero isobase of the lateglacial sea crossing the coast of Caithness near Berriedale, which is south of those sites described by Godard (1965) and Smith (1968).

Although no raised shorelines which could definitely be assigned to late- glacial times have been found, it is worthy of note that the high, steep and rocky configuration of much of the Caithness coastline would be inimical to the creation and preservation of evidence of the late-glacial submergence which "is ill-defined and was clearly short-lived" (Wright 1937). However, there are a number of re-entrants along the Caithness coastline where evidence of high-level late-glacial seas might have been expected to survive but even here effacement of such remnants by post-glacial seas, periglacial activity, or biological interference (e.g. agriculture) would be more than feasible.

The "raised beach" sites at the re-entrants of Dunbeath and Latheronwheel and a site of the same material at Achastle Bay consisted of exposures of beds of well-rounded to sub-angular pebbles of sandstone, gneiss and granite, some 0.5m in depth. These sections of highly-disturbed unconsolidated material which contrast markedly with the underlying compact shelly till, were levelled at the following altitudes: Dunbeath (Portormin headland): a number of small sections on the north side of the bay gave readings varying from 18.7m to 26.2m above Ordnance Datum.

Latheronwheel: sections on either side of the burn mouth and a notch in the drift on the south side were found to be at similar altitudes, namely 25.4m to 26.0m above Ordnance Datum.

Achastle: a small section on the coast (ND 230341) was levelled at 29.6m above Ordnance Datum.

All of these small fragmentary deposits are difficult to interpret, their origin and age being uncertain.

2. Low Level
In "suitable localities" in Caithness Crampton et alia (1914) saw evidence of a low-lying raised beach varying from 1.5m to 2.5m above sea level. Charlesworth (1957, Vol.2) recorded that the 8m beach fell to about 1.5m in south Caithness. Godard (1965) noted a low-lying raised shoreline whose altitude above high water mark decreased northwards from 3.5m at Lybster to 0.5m at Freswick Bay in north-east Caithness.

During the course of field work it was found that localities showing definite raised shoreline evidence were found at higher altitudes than had previously been suspected. To the north of Sarclet Haven is an interesting sequence of deposits (first described by Godard 1965) where two beds of marine pebbles are intercalated in angular debris, the whole resting on a raised rock platform. Godard regarded the angular rock fragments as periglacial in origin and the raised beaches as late-glacial. However, the adjacent cliff face is fault- shattered and coarse angular debris still falls on to the rock platform below, so it is possible that the two pebble beds are post-glacial in age. Apart from a deposit of flat cobbles at Dunbeath and the upper bed of marine pebbles at Sarclet (both-exceeding 6m), the raised shorelines of the east coast of Caithness are at low altitude above high water mark. The result of levelling raised shorelines (which often have associated rock notches cut at an equivalent height above Ordnance Datum) shows that their altitude declines northwards from Dunbeath and eastwards from Crosskirk. Because of the patchy nature of the raised beaches and the difficulty of attributing age to them, insufficient evidence is available to draw-a shoreline diagram.

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