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. Finer material was carried away by braided rivers and deposited on floodplains and in lakes. At times, river lain sediments were exposed to drying winds and formed sand-dune fields that compacted to form sandstone. Dune sandstones are visible in the cliffs at Broken Brough. You will notice a pattern in the cliff face known as 'cross-bedding'. There are several thick units made up of thinner, sloping, curved beds called foresets. These represent the forward face of a dune as it advanced down wind. Individual foresets can be identified due to small differences in the size and density of material in each layer. These rocks give us an insight into a long vanished environment. The direction of motion of the cross-beds shows the direction in which the dunes formed and therefore the direction the wind was blowing at the time.
The pattern of beds exposed in the sandstone cliffs show that they formed from sand dunes built up by winds blowing across a desert plain.
Directions
Broken Brough is in the South Mainland near Sumburgh
Take the A970 and turn off to North Town
Park in the lay-by just before the farm buildings, walk to the buildings and take the track to the left
Walk a few metres along the track then take the right hand track (before the 'beehive' structure) towards the wooden gate
Once through the gate turn left and follow the wall line until you have passed through two metal gates. Then turn right and cross the next fence
Turn left and walk along the coastal path until you pass through a gate
Continue until you reach the dune sandstone cliffs
Please note this walk contains a two-step stile
This site is very close to the Shingly Geo geosite