The Lava Plateau
In northern and western Skye the skyline is dominated by the stepped or 'trap' landscape created by lava flows from the volcanoes of Tertiary age which became active around 60 million years ago. These lava flows are horizontal or gently sloping and form distinctive flat-topped hills with stepped sides. The well-known MacLeod's Tables in Duirinish are an excellent example.
Individual lava flows can be up to 10 or 25 metres thick but they are not uniform throughout. At the top and bottom they are usually broken and slaggy with many amygdales (former gas bubbles now filled with minerals). The central parts are usually more solid, some with the distinctive columns which are features of the flows of the Giant's Causeway in Antrim and Fingal's Cave on Staffa. It is this contrast which results in the characteristic stepped landscape.
Accumulations of sedimentary rocks between the lava flows indicate that river systems and lakes were developed between volcanic eruptions, and plant remains within the sediment suggest a sub-tropical or Mediterranean climate. Where a long time elapsed between successive flows, red soils rich in clay developed which are similar to those developing today in wet, tropical or sub-tropical climates.
The plateau lavas are mostly basalts and were erupted rapidly, but with little explosive activity, from long cracks in the earth's crust which ran roughly from the north-west to the south-east. Volcanic ash deposits, which indicate more explosive activity, are rarely found, except at the base of the lava pile, which suggests a more dramatic initiation of the Skye volcano.