Ice, Wind & Water
Overlying the rocks are deposits that have come from the action of ice, wind and water during the geological period called the Holocene.
Deposits related to the meltwater and the bulldozing action of the glacier can be found at the margins of the strath. Better examples of these lateral moraines can be found of the eastern side of the Strath of Halladale.
Boulders transported by the glacier and deposited away from their parent lithologies are called erratics. Those that are placed on top of moraines and rock hills are called perched blocks. Many geologists have examined these to try and understand the pattern of glacial movement in a regional context. Examples of these occur on the hills between Reay and Armadale, including the hills above Strathy.
All of these help us to decipher what happened during the last period of glaciation to hit our strath. At that time we can imagine an environment much like Greenland today. Water melts from the glacier and washes through clay, silt, sand, gravel and boulders carrying these further down stream. Larger boulders can be placed upon deposits as the glacier recedes.
As the glaciers receded the weight of the glacier was removed from the landmass. This in turn resulted in the land rising relative to the sea level. The rise in sea level from the melt water was less than the rate at which the land rose - giving the false impression of sea level drop during the Holocene.
As temperatures rose at the start of the Holocene (11,000 year to present) there were significant changes in vegetation. Previously vegetation during the glacial period was limited to Arctic-alpine species and afterwards these moved to higher altitudes. Replacing the alpines were juniper, birch, heather and crowberry. Birch was replaced, based on pollen analysis, by heather at around 6200 years before present.
Throughout the last 11,000 years peat has gradually been accumulating as exemplified along the road from Forsinard to Melvich. Generally the climate has been wet and warm enough to encourage the growth of bog forming plants, yet cool enough to supress decomposition. Of course Sphagnum moss is the main constituent of peat bogs; it holds water, produces organic acids that help preserve organic remains and is able to absorb nutrients from water.
Above the cliffs the soil clings to the edge. In places horizontal ridges can be seen. These do not represent sheep tracks but slow, gradual soil creep related to soil slope failure.