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1992 Index Bulletins Index

Caithness Field Club


The problem with editing the Bulletin is, frequently, the lack of relevant material. I would like to suggest that, every time the Field Club holds an outing, the leader should prepare a hand-out in advance setting out the main purpose of the outing. This could then be used as an article in the Bulletin. The burden of writing this up would thus be spread over a number of people and over a number of months.

The Field Club trip by boat from Dunbeath to Berridale gave me a chance to study rock exposures which cannot be seen from inland sites. It is just a pity that the trip could not have been planned for the morning since the sun was in the wrong position to observe the rocks clearly. Perhaps the next time this could be borne in mind.

The Achanarras Horizon occurs in a road cutting at map ref. 177 309, about 2km. NE of Dunbeath. By analogy with central Caithness there should be two fossiliferous horizons below the above exposure, corresponding to the Wick and Helman Head fish beds. In the literature, Dipterus is reported from Berridale so a further fish bed was to be expected. The Ousdale mudstones have yeilded scales of Porolepis which suggests an Upper Emsian date for those rocks. Some kind of unconformity could be expected between the Emsian (Lower Devonian) and the Achanarras Horizon which is Eifelian (Middle Devonian) and ought to occur near Ceann Ousdale.

It was with high hopes that I sought some change in lithology which would reveal the Wick and Helman Head beds, the Berridale fish bed and the Junction between the Emsian and Eifelian. The rocks appeared, however to be a monotonous series of bedded reddish arkoses. No signs could be seen of the Wick and Helman Head beds. The arkoses persisted as a gently dipping series, involving enormous thicknesses of rock for 4 or 5 km. south-westward of Dunbeath. Then we get very heavily folded rocks, the folds of which become a gentle anticline for a kilometre or so. This is followed by a syncline which extends all the way down to Berridale. This violent earth movement which produced this folding may well represent the junction between the Emsian and the Eifelian.

No trace of a fish bed was seen at Berridale but the yellow arkoses persist to around Creag nan Bo (the Crag of the Ox). Here the cliff has collapsed into a great bolder scree. South of Ceann Ousdale the rocks appear more friable and they may represent the Ousdale mudstones. At Ord Paint we are probably seeing the Ord Granites and the fault scarp of the Brora-Helmsdale Fault in the background. Reefs of probable Kimmeridgian age extend for about half a kilometre NW of Green Table (the literature says they stop at Dun Glas). These Kimeridgian beds extend all the way down to Helmsdale.

The other surprising thing was the raised beach at Helmsdale which terminated abruptly at map ref. 037 155. The absence of the raised beach north of this point has never been satisfactorily explained.

Jack Saxon

Published in 1992 Bulletin