The gross form of the Shetlands evolved under non-glacial
conditions during the Tertiary. Two elements of the Tertiary
environment were important here: The Tertiary climate was much
warmer but less varied than that of the Quaternary. Maximum
warmth in Shetland was probably achieved during the Eocene.
Vegetation remains and latosols preserved between lava flows in
the Tertiary Igneous Province in western Scotland and Faeroe
indicate humid tropical conditions. Climates cooled during the
Oligocene but remained maritime sub-tropical to warm temperate
in character into the middle Miocene. Towards the end of the
Miocene, temperatures dropped and temperatures in lowland
Scotland remained generally close to today's. North Atlantic
cores indicate that relatively short periods of cold affected
Scotland during the Pliocene. The prevalence of warm and humid
conditions is significant for the evolution of the relief. Deep
chemical weathering is a highly effective process under these
circumstances, leading to etching out of