The Southwest Region - Southern England - page 71

FIG 70. Mass-flow terrace, looking westward from Cox Tor, Dartmoor. The terrace is in-
terpreted as being the result of down-slope movement under alternating freeze-thaw
conditions. (Copyright Landform Slides - Ken Gardner)
Rock basins are low-lying hollows in the granite topography draped with granite
weathering products. Sometimes these are dry and their floors are simply coated with
granite weathering materials. In other places the hollows are covered by peat, which is
often a feature of the higher and wetter parts of the granite hills. Under very wet condi-
tions, the hollows contain deep bogs or mires , with a reputation for being bottomless!
How these low hollows were excavated is a puzzle.
Topographic platforms, cut by storm waves during times of high sea level, have
been claimed to be present around the Dartmoor and Bodmin granite areas, although
they are not as distinctive as those discussed on the Land's End and Carnmenellis gran-
ites of Area 1. The Area 2 platforms are at heights of between 200 and 300 m above sea
level, but in the absence of dated deposits similar to the St Erth beds of Area 1, their
relevance to sea-level changes is open to doubt. Indeed, as mentioned above, terraces
have been recognised around the Dartmoor granite that are thought to be the result of
down-slope mass movement under freeze-thaw conditions, rather than due to sea-level
changes.
Landscape B: Killas and other Devonian bedrock
Apart from the granites, Devonian sediments make up the bedrock of the southern and
central part of Area 2. They consist largely of slates and mudstones with some sand-
stones, and are known generally as killas to distinguish them from the granites and oth-