|N E W S F E E D S >>>|
Caithness Field Club Bulletin
THE OLD RED SANDSTONE OF SHETLAND
In July 1990 I was invited to tutor at a summer school in Lerwick so I took the opportunity to stay on after the course to see as much as I could of the islands. My intention was to see as many ancient monuments as possible, visit as many classical localities in the Old Red Sandstone as I could, and do as much sketching and painting as possible. I duly went equipped with sheets 1 to 4 of the 1 :50 000 Ordnance survey maps, the Inventory of Ancient Monuments for Shetland, and the British Regional Geology memoir on Orkney and Shetland (l).
Having no previous experience of the Shetlands, I made Lerwick my base for exploration. The public transport system in Shetland operates on the assumption that people wish to travel into Lerwick in the morning and out of it in the evening, so much of my planning had to rely on tourist buses, which did not always go to the places I wished to visit, or did not allow for sufficient time to explore.
The Old Red Sandstone of Shetland is divided into three main formations: the Melby Formation lying to the west of the Melby Fault, the Sandness Formation and the Walls Formation, here treated as a single group, between the Melby Fault and the Walls Boundary Fault, and the south eastern group lying to the east of the Nesting Fault.
A number of fish beds occur in the Old Red of Shetland: the Melby fish bed, which is equivalent with the Achanarras Horizon, the Exnaboe fish bed which is faunally similar to the John o' Groats Sandstone, the Ness of Sound fish beds, the Mousa fish beds, the Sumburgh Head limestones, the Scat Ness limestones and the Bressay fish bed, which may be among the highest in the Shetland Old Red. The sketch map sowing the outcrops of the Old Red Sandstone rocks in Shetland is given in Fig. 1, after Mykura(l). These fish beds were of more interest to me than the structural geology or the depositional conditions of the rocks.
The Ness of Sound is an easy walk from Lerwick but torrential rain had turned the grassy slopes into quagmires; progress along the reefs was made impossible because of the numerous, but impassable geos which made climbing back up the cliffs necessary every few yards. I never did find the fish beds.
At the earliest opportunity I visited the museum in Lerwick in the hope that they would have a comprehensive collection of fossil fishes from the classical Shetland localities, and perhaps a little more information beyond what was given in Mykura. There was very little material in the collection. I suppose, when one is an enthusiast in some subject one finds it incredible that other people don't share one's interests. One of my pet hates is bus tours. From Greenland's icy mountains to India's coral strand the bus drivers rush you past the places of interest to show you what they want you to see; and there's always a compulsory photographic stop which is usually a good viewpoint and not in the least photogenic. Even when some place is picturesque they never leave you enough time to make even a thumbnail sketch. Among the chronicles of wasted time are hours spent at cafes and craft shops where, presumably, the driver or courier gets some kind of recompense from the proprietors. Funny-shaped rocks and wildish animals also take up valuable time. Even knowing this, I took a tour bus which included Melby at map ref. 186 579 on OS Map No. 3. Here we were treated to a visit to the spinning mill at Sandness. It was here that the weaknesses of the memoir were shown up; the famous Melby fish bed was not marked. I enquired of the local people where it could be found and, to my surprise, nobody had heard of it. In fact, they seemed to look on people with tacketty boots and anoraks who went off into the wild as mildly barmy. They supposed they went to look at birds or something. I only had about 45 minutes so there was no time to explore. I did create a rival interest to the spinning mill by showing some of the bus passengers that they could find gemstones on the foreshore. The bus driver took home a large rock full of gems, so now, perhaps, he will regale people with his new-found knowledge.
By comparison with the Melby Formation, Mykura treats the south eastern group of the Old Red in somewhat more detail. Again the actual fish beds are treated somewhat cursorily, possibly due to the fact that Willy Mykura had no great interest in the organic remains. The map, Fig.2, after Mykura, shows the locality of every fish bed.
A trip to Mousa was available, advertised as a visit to the famous broch and to see the wild life. If I was to visit the two fish beds which cut through the island I would have my work cut out, so the broch had to be treated somewhat cursorily. Stepping from the boat I made my way as quickly as I could towards the broch. Some of the younger people in the party took this as the opportunity for a race. But I was able to formulate a theory about the good state of preservation and the height of the broch. The internal diameter is quite small, only about 5.5 m, and the entrance is exceptionally large. When I entered the broch it was full of big girls, two to be precise, each about 2.5 m in diameter. It was impossible to get past them, as they bounced off the walls and each other. It was difficult to imagine how an extended family could live in so confined a space, even assuming more than one floor, and especially if they had been as big as those girls.
The first fish bed occurs in sheer cliffs just south of the broch where it was inaccessible and crops out again on the reefs at Green Head, or so the sketch map would have us believe. Someone had been splitting rocks at Green Head but I could find no trace of organic remains. The other fish bed is shown cropping out at the north east side of West Pool, but again I could find no trace of fossils. The memoir makes no mention of the fossils supposed to occur there, so I am extremely suspicious of the claim that they are, indeed, fish beds.
Ferries cross from Lerwick to Bressay fairly frequently but the fish bed is located at Bruntland on the north side of the Voe of Cullingsburgh, a round trip of, perhaps, 10 km from the pier on Bressay. The memoir states that the fishes in this fish bed are: Asterolepis, Holonema ornatum, and Glvptolepis paucidens. I have never actually seen either Asterolepis or Holonema. The Asterolepis of Stromness described by Hugh Miller in The Footprints of the Creator(2) turned out to be Homostius, as did the numerous reports of the same fish from Caithness. Asterolepis orcadensis has eluded me every time I have searched for it in Orkney, though the Orkney memoir(3) does give a text figure of this fish. The only description I have ever seen of Holonema is of an incomplete specimen. It has described by Obruchev(4). Because my time was strictly limited I had to choose between Bressay and the beds near Sumburgh. I chose Sumburgh for the simple reasons that there was a bus available to meet the Good Shepherd which sails from Grutness Voe to Fair Isle and, in the event of finding nothing, and my score had not been high so far, there was always Jarlshof to fall back on.
The more easterly of the fish beds lies at the foot of the cliff and it would have needed rock-climbing gear to have reached it. I couldn't find the more westerly bed - so I had to settle for Jarlshof. There is no service bus back to Lerwick so one has to go to Sumburgh Airport in the hope that there is an airline bus back to the capital. These buses cost a great deal more than the service buses.
There was one more fish bed in the Sumburgh area: the Exnaboe fish bed, and so I made the journey once again to Sumburgh and the obliging driver made a detour to take me into Exnaboe village. From here the route was over pasture land, barbed wire fences and burns to a place called Shingly Geo. The memoir states that the fishes present in this fish bed are: Asterolepis thule, Coccosteus sp. nov., Dipterus sp. Glyptolepis ?, Microbrachius dicki, Stegotrachelus finlayi, Tristichopterus alatus, and the invertebrate Estheria. There is something odd about this list. Microbrachius and Tristichopterus are found in the John o' Groats sandstones and in the Eday Beds of Orkney; it is possible that Asterolepis orcadensis also comes from this horizon although the Orkney memoir says otherwise. The Coccosteus nov. sp. indicates that the person who reported it was unsure of what he had found; Watsonosteus fletti would be consistent with The Eday Beds and this was confused with Coccosteus. Dipterus sp also means that the reporter was not familiar with the genus and I would have expected the fish to be Pentlandia. Estheria is now called Asmussia, so it is clear that the list is not Mykura's own, but culled from a very much earlier source.
The geo has, for one side, the steeply dipping bedding plane of the fish bed, the other side being the truncated beds. Someone had been hard at work on the fish bed which was convenient for me since I seldom carry tools, regarding indescriminate collecting to be essentially a destructive process like bird nesting or picking rare flowers; rather worse, in fact, since fossils cannot regenerate! I found Dipterus, and it was Dipterus, not Pentlandia.. The two genera must have an overlap as I have suspected for several years. I found Glyptolepis, Microbrachius dicki and Stegotrachelus finlavi. I brought away two specimens of Stegotrachelus and four of Microbrachius, though they were incomplete. I was delighted to have them since they were lacking from my small collection.
Near the Exnaboe fish bed there is a broch, number 1147 in the inventory of ancient monuments. It is little more than a grass-grown mound and of no special note. Immediately adjacent to it on the south side there is a curious structure consisting of a large circle of small stones with parallel rows of stones inside it. I have never seen anything quite like it and it is not described in the Inventory. It would have taken me quite a long time to have mapped it adequately and I had about a 7 km hike to the terminal building at Sumburgh in the hope of a lift back to Lerwick. So this enigma remains to be described in the future and, probably by somebody else.
Of course I visited quite a lot of other places of interest and collected rocks and minerals, I visited Yell and Unst, Muness and Scalloway Castles, and found gemstones in the andesitic lavas and tuffs south of Esha Ness lighthouse and, of course, visited the Sullom Voe oil terminal.
If ever I get to go back to Shetland I will make every effort to find the Melby fish bed, and I hope to be better prepared. Let's Hope so!
(Figs 3 and 4 appear here)
2. Miller, H., Footprints of the Creator, Edinburgh, 1849.
3. Wilson, G. V. et al. The Geology of the Orkneys, Mem. Geol. Surv., Great Britain, HMSO, 1935.
4. Obruchev, D. V., Osnovy Paleontologii, Beschelyustnye, Ryby, Izdatel'stvo "Nauka", Moscow, 1964.