Canna and Sanday - Where Rivers and Volcanoes Meet
Canna and Sanday are composed largely of lavas, part of the major lava field that is exposed in northwestern Rum and extends to northern Skye. These basalt lavas were probably erupted from a major volcano on what is now the Isle of Skye. But what makes Canna of particular interest is that the area was traversed by fast-flowing rivers at the same time that the volcano was erupting. Great thicknesses of boulder conglomerate were deposited by this river. The boulders were rounded as they were carried along in the fast flowing river currents. Some are over a metre in diameter, indicating the strengths of the currents involved. Pebbles in these deposits have been matched with bedrock from Skye, suggesting that the river flowed from the north. These rocks were first studied by some of the early geological pioneers of Scottish geology, such as Archibald Geikie in 1897 and Alfred Harker ten years later.