We are fortunate, in the British Isles to have some of the most complex and varied geology for any area of comparable size in the world. The northeast corner of Scotland is no exception, though it is perhaps less well known than other areas to many geologists simply because it is remote. Surely, however, this magnificently produced field guide will encourage geologically-minded visitors to explore this splendid region, and to study its unique rock successions.
This book is an updated version of the excellent guide of 1993 by the same authors and editors, and with the same title. Although the basic plan and the excursions are only modified in places, the bulk of the illustrations in the new guide are in full colour, and have reproduced splendidly. Dunedin Press does these things very well, rendering this guide even more useful as well as attractive.
The book begins with an introduction to the geology of the area, which extends south of Brora, and west of Strathy Point. The oldest rocks, the metasedimentary Moines, deposited some 900 Ma and metamorphosed later, form the basement, and are present in the western part of the area, and as small inliers further east. The great three-humped mass of Scaraben forms the easterly extension of the Moine rocks. They are intruded by the Strath Halladale and Helmsdale granites, of Caledonian age. The latter, close to the sea forms the high ground of the Ord of Caithness, defining the southern boundary of that county. Somewhat further north a line of improbably shaped mountains composed of Lower Devonian conglomerate thrust sharply into the sky. Northwards again the ground becomes flatter and gently undulating but sloping northwards and eastwards towards the sea, to terminate in spectacular sea-cliffs and stacks. This land is underlain by some 4km thickness of Middle Devonian lake deposits, replete, at certain levels, with fossil fish. Upper Devonian sandstones are preserved only on Dunnet Head, the most northerly point of the Scottish mainland; equivalent rocks form most of Hoy, in the Orkney Isles, seen across the Pentland Firth. In the southeastern region the great Helmsdale Fault, hugging the coastline, passes onto land, separating the Devonian from a coastal strip of Triassic and Jurassic, the youngest rocks in the area. These provide an onshore equivalent for productive oil reservoirs lying eastwards, under the sea. Evidence of the Quaternary is limited, but there are relics of two glaciations.
The structure of the region is fairly simple, the Middle Devonian is folded into a gentle east-west anticline, seen on the east coast at Sarclet, and apart from the Helmsdale Fault there are smaller faults in Caithness, within the sedimentary sequence. Igneous intrusions, apart from the granites referred to, are minor and few.
Following the Introduction, which finishes with a fine section on economic geology, discussing, amongst other issues the still extant, though greatly reduced Caithness Flagstone industry. Then comes a useful Excursion Planner, with map, and finally the excursions themselves. Six areas are covered, each distinguished by a coloured strip along the top edge of the book.
The first four excursions, by Andrew Hurst and Nigel Trewin, cover the coastal area to the southeast, particularly the Mesozoic beds east of the Helmsdale Fault and the Helmsdale Granite. The penultimate excursion has five separate itineraries chiefly in the Middle Devonian, in the northern part of Caithness. The first itinerary covers the famous Achanarras Quarry, where Nigel Trewin has done such sterling work on the succession and ecology of the fish bed, and the Dirlot region where Moine rocks come to the surface. The second itinerary deals with the east coast exposures of John o'Groats, Duncansby and Sarclet, and the only extra locality which might have been included is the spectacular inlet at Whaligoe, where three regular cycles are seen in the cliff, one above the other. But the cyclicity can be very well seen along the northern shore, from west of the Upper Devonian Dunnet Head to Brims Ness (itinerary three). The fourth itinerary is concerned with basin margin deposits at Baligill and Red Point, with further fish beds a little to the east at Sandside Bay.
Excursion six – Kildonan Gold! Here are Moine rocks, shot through with granite and quartz from which came the gold. There was indeed a substantial gold rush in 1868–69, as is illustrated here in old engravings. One can still pan for gold here, and Clive Rice in this fascinating chapter gives instructions on how to do so.
This is a lovely book, easy to read, but a mine of information, and beautifully produced. So much of the geology is quite different from that in other parts of Europe. If you have never visited this remarkable area, may I advise you that the long journey is well worth while for geology and scenery too. And take this book with you!
