Ancient Loch
The rocks to the east of the river represent as significant contrast to those in the west. East of the river the rocks form part of the same sequences that has resulted in the flat lying nature of Caithness. These rocks are termed Caithness Flagstones and were formed in a series of fresh-water lochs during the Devonian geological period, often terms Lake Orcadie. The series of lochs extended over Caithness, Orkney, Shetland, western Norway and the Moray coast.
The Lower Devonian was deposited on the irregular basement of post-Caledonian land surface. Before these rocks were deposited there was a long period of erosion and weathering. Mountains and hills to the west were cut by rivers and alluvial fans in a fairly hot and arid climate. Flash floods resulted in dumps of sandy material on the (sometimes dried out) lake floor. The area of the Baligill Outlier represents the westernmost margin of the Orcadian lake system.
The Middle Devonian lithologies were deposited in the main period of lake development. The rocks are predominantly grey or green in colour and form a series of cyclical deposits recording deposition in a lake of fluctuating depth and extent.
During deep lake periods dark organic-rich laminated beds were deposited. These contain the fossil remains of boney-headed fish that swam in the lake. The fish beds, as they are termed, are correlated to the fish-bearing layer at Achanarras near Spittal in Caithness.
From the slipway at Port Skerra one can see in the cliff face opposite the relationship between the Devonian rock are the underlying basement. The irregular surface of gneiss is overlain unconformably by conglomerates and sandstones probably representing the deposits of flash floods.
From the slipway at Port Skerra one can see in the cliff face opposite the relationship between the Devonian rock are the underlying basement. The irregular surface of gneiss is overlain unconformably by conglomerates and sandstones probably representing the deposits of flash floods.
Samhchair