Orkney Shores – Grit Ness 1

It is a short walk from the Knowe of Stenso Broch archaeological site. A few steps from the parking area (GR 371265) takes you past an old abandoned stone building to the beach and the pier of Grit Ness. It lies on the north coast of West Mainland in Orkney and looks out over the water of Eynhallow Sound to the small island of Eynhallow and the larger island of Rousay beyond. The whole area is underlain by gently sloping layers of Upper Stromness Flags from the Devonian Period  but these are partly covered by sand and weed. On the low cliff of a few metres height at the top of the beach glacial till overlies the rock with windblown sediments above, creating a space where luxuriant vegetation and wild flowers grow. Although visiting in June, the plants and weather made it seem more like spring. Lots of white lacey flowers and super-pink red campion. The line between land and sea is obviously vulnerable and has been reinforced east of the pier at some time by an unusual type of beach armour in the form of intertwined rusty iron rings. I wondered if this might be a remnant of some World War II structure. Further west there are areas of crumbling flagstone beneath the sand where there is no shore reinforcement.

The bedrock flagstone of the Grit Ness shore has broken up into large slabs in places, and these in turn have broken up into smaller cobble sized pebbles accumulating elsewhere. Sand is spread out in patchy randomness over the shore, giving rise occasionally to a peculiar hummocky terrain. I have not come across anything like it before, and am not sure how it is formed, but it may be a combination of the underlying topography and a peculiarity of the tides and currents. It looks as if someone has been extensively bait-digging. Rock surfaces on the lower shore are partially covered with dark olive fucoid seaweeds like bladderwrack; while vivid green soft gut-weed coats separate distinct areas of sand and stone.

Most of the flagstone on the beach has characteristic natural patterns. These rocks formed at the bottom of a large lake which was prone to drying out. This left the wet sediments of the lake bed periodically exposed to air, and they dried out giving rise to roughly polygonal dessication cracks. The cracks subsequently became filled-in with a contrasting colour of new sediment arriving at a later stage. The drying out patterns are on a varying but fairly large scale. There are also many smaller marks. I first thought that they were trace fossils resulting from the burrowing activity of worms or other small marine invertebrates in the ancient muds before they turned into rock. I discovered that these are mostly (but not entirely) pseudomorphs. Pseudomorphs look as if they are fossils or ichnofossils but are the result of gypsum contained within the rock dissolving out at some stage in their geological history and being replaced by other substances of a contrasting colour and texture.

The sandy areas of the beach were not only covered by the large mounds and hollows mentioned before but also were covered in thousands of worm casts. Marine worms, presumably Arenicola, obviously thrive here and are very active between tides judging their abundance and the size of the casts. Even where there is only a thin covering of sand over the flat rocks, casts could be found running in straight lines along the surface where the worms were using the natural cracks and crevices between the flags to bury deeper.

Click on any of the images above to enlarge and view in a gallery with details.