The fascinating geology of the Stromness West
Shore is revealed in its very well preserved features.
The spectacular coastline at Yesnaby.
Lake Orcadie was Orkney's prehistoric lake,
situated on the Stromness West Shore.
Geology of Orkney
The rocks of Orkney are dominated by flagstones and sandstones deposited in a huge fresh water lake. They belong in time to the Devonian (Old Red Sandstone) period (416 – 359 million years ago). The sediments of Lake Orcadie are superbly exposed along the many cliffs and shore platforms and so Orkney gives us one of the best examples of a Devonian lake basin in the world. The lake teemed with life, leaving many fossils, including wonderfully preserved fossil fish, and periodically dried out as desert conditions set in. Volcanic activity left lavas and vents filled with agglomerate and ash. Younger Permian (250 million years old) intrusive lamprophyre trap dykes are numerous. The oldest rock exposed in Orkney is the Precambrian Basement Complex. These outcrops represent the tops of island hills emerging from the early Lake Orcadie located in an equatorial and mid-continental desert.