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Geology

Solid Geology

Caithness owes its low lying undulating landscapes to the middle old red sandstones that formed from successive episodes of deposition on the bed of a shallow, but extensive lake known as Lake Orcadie. The depth and conditions of the lake varied, as the climate cycled between wetter and dryer periods. This is reflected in the rocks that exhibit repeated cycles of stratification each cycle representing about 100,000 years and having five distinctive divisions of composition, including thin lamina of calcareous siltstone. Since the rocks were first laid down they have been subject to cracking and upheaval and lateral displacement referred to as faulting.

The solid geology of the Yarrows area comprises the Clyth and Lybster subgroups of the Wick beds of the Caithness flagstones, a facies of the middle old red sandstones, the Clyth beds underlying the Lybster group.

Drift Geology - Loch of Yarrows

Solid geology of the Yarrows area

The geology that gives form to the landscape as we experience it comprises the solid geology,  the rocky bones of the land, and the drift geology  the sediments and soils that clothe the rocky skeleton.



























Caithness owes its low lying undulating landscapes to the middle old red sandstones that formed from successive episodes of deposition on the bed of a shallow, but extensive lake known as Lake Orcadie. The depth and conditions of the lake varied, as the climate cycled between wetter and dryer periods. This is reflected in the rocks that exhibit repeated cycles of stratification each cycle representing about 100,000 years and having five distinctive divisions of composition, including thin lamina of calcareous siltstone. Since the rocks were first laid down they have been subject to cracking and upheaval and lateral displacement referred to as faulting.

 

The solid geology of the Yarrows area comprises the Clyth and Lybster subgroups of the Wick beds of the Caithness flagstones, a facies of the middle old red sandstones, the Clyth beds underlying the Lybster group.

Soil profile at Oliclate Mesolithic site

The western aspect of valley that encloses the Lock of Yarrows is characterised by a series of escarpments associated with three parallel faults that run approximately north south through the area. A fourth fault, further to the east, runs north - south, through the centre of The Loch of Yarrows, terminating at the Clyth- Lybster flagstone subgroup transition.

Exposures of the faulted Clyth beds occur at several points on the trail, dipping circa 10 degrees to the south. The beds form part of the lower division of the Caithness flagstones.

The diagram indicates the principle deposits of boulder clay, or till as it it now known, deposited by the receding ice of the last ice age. Subsequently, a thin mineral soil formed  over the till which was overlain by peat as the climate deteriorated.

 1) British Geological Survey Latheron Scotland Sheet 110.

Faulting and Drift geology

The soil profile at the Mesolithic site at Oliclate indicating peat overlying a mineral soil and glacial till. A vertical fissure can be seen indicating a period of extreme desiccation of the mineral soil horizon.

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