erosion surfaces  domes  tors  valleys

deep weathering  preglacial drainage                

The Howe of Cromar, looking towards Lochnagar (above)

The Tomintoul basin from Google Earth (right)

The Mine Mhr, the high-level basin above the trough head of Gleann Einich. This ancient hollow captured snow and fed ice into the Einich and Eidart during the Ice Age. Mine Mhr

Skiing out of the fastnesses of the Avon Embayment

Linton's (1950) map showing the outline of the Cairngorm Granite (stippled) and the three large embayment that bite into the main plateau.

Looking back to Beinn Bhreac from Moine Bhealaidh.

Part of the Mine Bhealaidh, a high level basin in the Cairngorms. Moine Bhealaidh Streetmap extract.

Basins

Definition: an area of relatively low ground that is enclosed largely by the surrounding hills and ridges

Topographic basins or howes occur widely in northeast Scotland. Fine examples occur along the Don and include the Howe of Alford. The Dee valley also shows a succession of narrow, gorge-like sections and open basins. The Howe of Cromar and the Lumphanan Basin are two of the larger basins.

These basins are preglacial forms. Some have had a very long history, with the Cabrach and Tomintoul Basins, for example, retaining outliers of Old Red Sandstone. The basins are often centred on rocks of low resistance to chemical weathering. It seems that the basins have formed in response to millions of years of differential weathering and erosion, with gradual deepening as the preglacial rivers removed the products of weathering. The final phase of deepening was by glaciers during the Quaternary (Hall and Bishop, 2002).

The highest representatives of these basins occur in the Cairngorms. Linton (1950) identified the huge embayment on the north side of the Cairngorms as a topographic basin that was unrelated to the shape of the granite mass - this he named the Glen Avon Embayment. He also recognised that the outline of the Cairngorm Granite pluton does not correspond with the edge of the plateau in two other locations - Glen More and hills around Sgr Mr.

The preglacial form of the basins of the great mosses is also evident from the surrounding summits. The Mine Mhr (seen above) is a basin at ca. 900 m OD developed on schists that retains weathered rock on its floor. The Mine Bhealaidh is a more complex form, partly developed on diorite and schist. Its floor is deeply incised by the deep glacial valleys of Glen Derry and the Dubh Ghleann. Both basins acted as the sources of the Dee prior to glaciation and drainage diversion.