During the Devonian Period nearly 400 million years ago, rift basins formed in and around the Caledonian Mountains as the landmass of Euramerica was pulled apart by tensional forces. Shetland lay at the edge of the Orcadian basin in the eroding mountain foothills. Fast flowing rivers washed boulders, pebbles, sand and mud down the mountains, dumping large stones at their base and carrying finer material onward to be deposited on floodplains and in lakes. Lakes are represented in the rock sequence by beds made up of thin layers of fine sediment and impure limestone. Some of these strata, known as 'fish beds', contain large numbers of fossil fish. These are often almost intact, the dead fish having sunk into the depths of the lake where lack of oxygen meant that there were no scavengers to feed on the remains. Each layer in the sediment represents the sediment accumulated over one year so the length of time represented by a fish bed can be established. The fish communities in the lakes changed over time as new species evolved and old ones died out. Geologists use this information to work out age relationships between Devonian rocks in various parts of Scotland. Note that the collecting of original geological material such as rocks, minerals, and fossils is discouraged within the Geopark. If you are lucky enough to spot a fossil please do not attempt to remove it. We would appreciate it you would report your find to the Geopark (info@shetlandamenity.org) so that it can be properly recorded.
Two species of fish were first discovered at Shingly Geo - Stegotrachelus finlayi, an early member of the ray-finned fish family that includes most modern fish, and a species of Coccosteus, a primitive armour plated fish. Stegotrachelus finlayi has not been found anywhere outside of Shetland.
