The gross form of the Cairngorms 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 northeast 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 actual temperatures at high elevations in the Cairngorms during the Tertiary remain unknown but it is likely that long-lying snow only became a feature of the mountains during parts of the Pliocene and in the Quaternary.
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 rich in china clay, 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 Cairngorms, the degree of uplift is uncertain but it must have been considerable. The present terrain reaches 1300 m asl, despite 50 million years of denudation. Significant differential movements took place across northeast Scotland, with the lowlands of Buchan remaining close to sea level. The present elevation of the Cairngorms may be partly a reflection of a late phase of uplift in the Plio-Pleistocene.
Tectonic activity in the later Tertiary was episodic, with periods of calm interrupted by uplift during the late Oligocene and Pliocene. Again, this uplift varied across northeast Scotland, with reactivation of major faults in the Monadhliath. Tilting of major erosion surfaces towards the Moray Firth and the North Sea produced the ramp-like plateaux of the Monadhliath and the Mounth .