Caithness Field Club

Caithness Field Club Bulletin
2006

Introduction
The geology of Caithness is essentially that of cyclic sedimentary rocks deposited in playa lakes and desert sequences. The rocks were laid down in Devonian times, about 370 million years ago, in a great basin named the Orcadian Lake, The basement and margins consist of crystalline and metamorphic rocks. Frequently the sedimentary rocks contain barren breccias and mudstones derived from these crystalline precursors. This guide has been written to let the visitor know where typical rocks and fossils can be found.

The Baligill Outlier
Leave the A836 at the small signpost for Baligill opposite the bus shelter; keep to the metalled road. When you see the disused lime kiln, park off the road but do not obstruct the Passing Places on this single track road. Enter the overgrown derelict quarry at the gate by the lime kiln (map ref NC852656)
The Baligill outlier is a green oasis in the heather-covered landscape of north east Sutherland. It is included here because, geologically, it belongs to Caithness. The stone was taken from the quarry for lime burning. There is an upper fish bed to the east and a lower fish bed to the west. The commonest fish here is Thursius macrolepidotus, but Coccosteus cuspidatus, Gyroptychius agassisi, Cheirolepis trailli and Pinnalongus saxoni also occur.

Portskerra
Leave the A836 at Melvich and follow the signpost to Portskerra Harbour; there is limited parking here. The unconformity between the gneisses of the basement and the Old Red Sandstone, which passes upwards from breccias into bedded sandstone, is clearly shown. From the nature of the exposure it can be seen that the original basement was extremely rugged.

The Reay Diorite
On the north side of the road just west of the woods of the Sandside estate there is a small quarry. This is a good exposure of the Reay Diorite, which was quarried extensively, most recently for the new pier at Scrabster for the Roll-on -Roll-off ferry to Orkney.

Sandside
At Reay follow the signpost for Sandside, there is a small car park near the toilets and a large one near the harbour. There are warning notices that radioactive particles have been found and that nothing should be removed. The beach is monitored regularly.
A number of fish beds occur on both sides of the bay, the commonest of the fishes being Thursius macrolepidotus. Mesacanthus and Pinnalongus saxoni are also found.
There is a burial vault in the old graveyard which contains a Pictish carved stone.

Brimsness
Leave the north side of the A836, (at map ref. ND080711) down a farm track which passes the ruins of Brims castle with its Barmkin. Access to the sea shore is through a farm gate. Fragments of osteolepid fishes are fairly common.

Holborn Head
Park the car at Scrabster Harbour and walk to the disused lighthouse, then take the signposted footpath to the headland (map ref ND109716). At the very end there is an Iron Age promontory fort which had natural defences in the form of holes and geos which have formed along lines of weakness due to faulting. It was here that Hugh Miller, author of 'Old Red Sandstone', saw a specimen of Homostius part way down the cliff and asked Robert Dick to recover it for him. The nearby Clett Rock should be visited if only for the colonies of sea birds which nest there.

The Pennyland Beds
Pennyland Farm (map ref. ND109688) was the birthplace of William Smith the founder of the Boys Brigade and a memorial to him is on the south side of the A836. The farm land extends to the cliffs along which the footpath called Victoria Walk runs.
The shore reefs from the beach at Thurso westwards to the ruins of the Bishop's Palace are only accessible at low tide. Tide Tables are available from the Harbour Office at Scrabster. It is a very interesting section with many fish beds exposed by repeated faulting. Several geos have been formed along lines of weakness (faults and joints) and small caves also exist, the most notable being Samson's Coach House and Namie Geo, so called because of the numerous inscriptions carved on the walls. The common fossils found on the reefs between Thurso and Scrabster are Millerosteus minor and Thursius pholidotus. There are two exposures of false bedded sandstone, one at the sea stack known as Needle E'e and one on which the ruins of the Bishop's Palace stands. East of the Bishops Palace and adjacent to Victoria Walk is the roofless ruin of the mortuary chapel belonging to the Murray family.

The Kirk Ebb
The reef to the east end of Thurso beach, known as the Kirk Ebb, is only accessible at low water. A single fish bed is exposed which has yielded fragments of Homostius milleri and skulls of Dipterus and Gyroptychius milleri.

Thurso East Shore
Car parking is available in Sir Archibald Road, a bust of Robert Dick is mounted on the wall at the road entrance.
Thurso East Shore has a single fish bed exposed on the slabs below the ruins of Thurso Castle, fragments of Homostius, Dipterus, Gyroptychius milleri and Glyptolepis have been found. Ripple marked beds are common as are desiccation cracks. As you travel north east along the shore a small fault raises the fish bed above head height. Crossing the footbridge from Sir Archibald Road will bring you to Wilson Street, just past the Scout hall. The first house on the right has a plaque over the door. This was the house occupied by Robert Dick, geologist and botanist.

Murkle Bay
Access to Murkle Bay (map ref. ND169695) may be difficult owing to an electric fence at the sea end of the road to the derelict farm. The reefs mapped as the Spur contain numerous specimens of the invertebrate Asmussia murchisoniana. The reefs to the east contain Thursius pholidotus and Millerosteus minor.

Castletown
Castletown is known as the Flagstone Village. It is here that the Caithness flagstone industry began. After many years of successful operation it began to decline in the early 20th century.
Take the road from the centre of the village and follow the signposted track around the derelict site.
Flagstones were quarried in the village and a windmill was used to pump water from the workings.
The flagstone was brought to the cutting frames near the shore which were powered initially by two overshot water wheels. A harbour was built close by and the flagstone was exported pretty well all over the world by schooners.

Duncansby Head
Duncansby Head (map ref. ND406735) is a good viewpoint and has spectacular geos. A footpath runs
south, from which the Stacks of Duncansby can be clearly seen.

Ackergill
Just west of Wick Ackergill (map ref ND360546) is signposted from the A99. Ackergill Tower is the oldest inhabited house in Caithness and is now a hotel. Walk along the shore towards the Tower. The reefs below contain Millerosteus minor. To the right of the old lifeboat ramp is John O'Groat sandstone with Watsonosteus fletti and Microbrachius dicki.
At Ness of Quoys (map ref. ND345735) we again encounter the Mey sub-group with Thursius pholidotus and Millerosteus minor.

Noss Head and Castle Girnigoe
From Wick take the road to Noss Head (map ref ND389550). A small cliff top quarry has yielded Dickosteus thrieplandi. Park at the car park and take the footpath to the ruins of castle Girnigoe ( map ref ND380550). Measures are being taken to make the ruin safer for public access.

South Head, Wick
Follow the signs south of Wick river for Auldwick Castle. Stop at the sea water pool known as the Trinkie. Walk down towards the pool and look back at the low cliff section. Here you can see a fish bed sloping downwards. It is not possible to collect at this site but, in the past, it yielded Thursius macrolepidotus.
Walk on to the castle of Old Wick. The castle is of great antiquity, being a simple square tower, ruinous on the seaward side.

Weydale, Cairnfield and Stonegunn
These derelict quarries are about 4 km from Thurso, at Weydale ( map ref. ND145652), Cairnfield (map ref ND150650) and Stonegun (map ref ND160660). Osteolepis panderi, Dipterus and small acanthodians are common.
The line of the old horse drawn railway can be traced from Weydale to Thurso East where the flagstones from these quarries were sawn up and stored pending the arrival of the schooners which were used to export them. The flagstone works were operational until the 1950's.

Spittal
Spittal Quarry (map ref ND173540) is a working quarry. Fossils are not usually found in the flagstones but in the fine laminates which were deposited in stratified lakes. The fish bed at Spittal was adjacent to the road and yielded the large arthrodire Dickosteus thrieplandi. The quarry is most famous, however, as the source of the largest cephalaspid ever found - Cephalaspis magnifica.

Achanarras
From the A9 south of Spittal follow the signposts to Achanarras Quarry. The quarry is about 2 km from the B870 up a gated farm track. There is a parking place on this track which is still about 1 km from the quarry (map ref. ND150544). Please follow the Country Code and close all gates. A permit to collect fossils must be obtained from Scottish Natural Heritage at Golspie. This site is world famous in having more genera and species than any other known Devonian location. Dipterus vallenciennsi, Coccosteus cuspidatus, Palaeospondylus gunni and small acanthodians are common. The shadowy agnathan Achanarella is also locally common.

Dirlot
If you have visited Achanarras you could follow the B870 to Westerdale and continue straight along, crossing the river bridge, reaching after 2 km a track on the left which passes through a sand and gravel quarry. (For those interested in Quaternary Geology this quarry is part of the kame system which can be followed across country for several kilometres.) Continue along the track until it turns a sharp left at a derelict cottage and park off the road. Go through the gate and follow the track to the small graveyard. On an isolated mound there are the remains of an old castle. Below the castle is a deep pool in the Thurso river (map ref. ND125485). The gorge has a small inlier of the Moine schist overlain unconformably by basal breccia of Old Red Sandstone age. This breccia is covered with stromatolites.

Westerdale
At Westerdale take the B870 towards Scotscalder. There is a small quarry, (map ref. ND112519), which contains Thursius macrolepidotus.

Leavad
At Leavad (map ref. ND173460) there is a deposit of Cretaceous sand associated with a glacial erratic. The sand was been quarried for use as the abrasive in the cutting of Caithness flagstone. The size of the erratic was shown by drilling to be over 200 m. long, 140 m. wide and 8m. thick. There is a cart track from the A9 at Tacher to the sand pit.