Geology Reference
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appears to be of the same origin as flared slopes, and is a manifestation of soil moisture attack in
the scarp-foot zone.
Many examples of basal fretting have been noted in tropical and subtropical, arid and semi-arid
regions, where scarp-foot water concentrations are highly significant. But they are by no means
restricted to such areas. Thus, on Dartmoor, southwestern England, isolated blocks and menhirs
(Fig. 7.16a) display basal fretting and/or basal depressions. The basal fretting around the menhirs
argues a rapid rate of development, at least in the geological context.
In some areas, basal indentation occurs at the margins of ephemeral lakes and may be caused by
either weak wave attack, or weathering by saline lake waters, or a combination of the two. Jutson
(1914), described what he called billiard-table surfaces backed by basally notched cliffs from the
Salinaland division of Western Australia, and similar forms have been observed in granite gneiss
at the margins of Lake Greenly, on southern Eyre Peninsula, South Australia. But these are
(c)
(d)
Figure 8.11.
(c) The Cumberland Stone, from which the Duke of that name directed the Battle of Culloden
Moor in 1745 (British Tourist Authority); (d) on large residual boulder with closely-spaced and
strongly developed vertical fractures, Cassia City of Rocks, Idaho (Mueller and Twidale, 1988).
 
 
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