At Muckle Head (HY 213053) on the north coast of Hoy beach sediments occur at 6 m OD that must pre-date the last ice-sheet glaciation of the islands (Wilson et al., 1935; Sutherland, 1993; 1996). The sequence of sediments can be summarised as:
The basal gravel is a beach deposit. Overlying the beach gravels is a periglacial slope deposit (‘head’) and a glacial till. The sequence of events appears to be (Sutherland, 1993):
1. high sea level and deposition of the beach
2. sea-level fall,
3. onset of periglacial conditions with the formation of the slope deposits,
4. invasion of the area by ice and deposition of the till,
5. ice retreat and solifluction of the upper layers of the till in a cold climate
6. deposition of the capping sands.
The age of the deposits is unknown. The beach sediments clearly pre-date the last phase of ice-sheet glaciation of this part of Hoy which would make them pre-Late Devensian in age. The adjacent geo must also be an inherited feature.
To the east along the coast near Selwick (HY 225055) there is another exposure of raised beach gravels overlain by till. The gravels can be seen to rest on a bevelled rock surface which may be part of a raised shore platform.