The colour of the tills on Orkney is largely a reflection of the rocks over which the ice had passed. The red marls and sandstones of the Eday Group give a distinctive red till and erratic clasts of red sandstone are a major component of these tills in the eastern parts of Westray. ...
On the main tools for reconstructing the glacial history of an area is to examine the local stratigraphic record. Tills are firm indicators of the former presence of glacier ice and their fabrics and erratic content provide information about the direction of former ice movement. Where tills are inter-bedded with other sediments, such as meltwater or periglacial deposits then a sequence of events can be built up.
In a few parts of Scotland, including northern Lewis, Berwickshire, Buchan, Caithness and Orkney, the last ice sheet flowed across marine sediments before moving on to the current land area.
Much of the low ground of Orkney is blanketed by a layer of glacial deposits left directly by the last ice sheet. Termed boulder clay in the 19th century on account of its common mix of boulders in a matrix of sand, mud and clay, this material is now referred to as till.
Moraines are landforms created at the margins of glaciers by the melt-out of debris from the glacier and by the bulldozing action of the ice. Moraines are classified according to their position relative to the former glacier: terminal, medial and lateral.