The gross form of Caithness evolved under non-glacial conditions during the Tertiary. Two elements of the Tertiary environment were important:
The Tertiary climate was much warmer but more settled than that of the Quaternary. Maximum warmth in Scotland was probably achieved during the Eocene. Vegetation remains and latosols preserved between lava flows in the Tertiary Igneous Province 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 differences in bedrock resistance within the landscape. The deep weathering profiles would have been highly kaolinitic, as in tropical climates today and as shown by the composition of contemporaneous sediments in the North Sea. These kaolinitic weathering mantles have been stripped away, latterly by ice sheets in the Quaternary but remnants appear to survive in the Buchan lowlands, together with residues of Chalk flints.
The main tectonic events to affect Scotland during the
Tertiary are slowly becoming clearer (Hall and Bishop, 2002).
At the end of the preceding Cretaceous period, Scotland was a terrain of low
relief, unable to supply much sediment to the surrounding Chalk seas. Lowland
areas emerged with a cover of chalk. The main phase of uplift throughout
Highland Scotland was in the late Paleocene, corresponding to the passage of
western Britain over the hot spot that now feeds the volcanoes of Iceland. In
western Scotland, vertical movements around the igneous centres were of the
order of 1-3 km. In the Northern Highlands, the degree of uplift is uncertain but it
must have been considerable. The present terrain reaches 1100 m asl, despite
60 million years of denudation. Significant differential movements probably
took place across northern Scotland, with the lowlands of Caithness and Orkney remaining
relatively close to base
level. The present elevation of the plain of Caithness may be a reflection of a late
phase of uplift in the Plio-Pleistocene.