Tropical landforms
569
tors as originated by weathering and removal under periglacial envronments.
Mineralogical analyses of the Dartmoor grus make evident the absence of alteration
of feldspars and a low clay content (Doornkamp, 1974). Consequently, in European
latitudes a "sandy weathering product" can form (Bakker, 1967), which can involve
producing blocks.
King (1948) proposed that tors, the same as dome inselbergs, originate by slope retreat
in arid and semiarid climates, giving rise to a pediment at their feet. Similar ideas,
although developed for periglacial environments, were elaborated by Czudek (1964)
(Figure 8.11).
From the above discussion, there is no doubt that there exist several hypothesis for
explaining the origin of such boulders. Two main tendencies can be deduced: one related
to deep weathering and later erosion (the two-stage hypothesis of Linton) and the other
related to slope retreat in warm and cold deserts.
5.2. Domed inselbergs (bornhardts)
As previously noted, the term bornhardt is due to Willis (1936), for defining crystalline
domes in the honour of the German explorer Bornhardt (1900), who first described
inselbergs. They have a dome form and develop on resistant massive rocks, mainly
granites, although also on sandstones and conglomerates in central Australia. Twidale
(1982a) considered the Mallos de Riglos conglomeratic monoliths in the Spanish
Southern External Pyrenean ranges (Figure 21.35), to be bornhardts. This assumption
can be extrapolated to the conglomeratic mountains of Montserrat, Montsant,
Figure 21.35. Monoliths developed on massive horizontal conglomerates in the southern limit of the
external Pyrenean ranges, in contact with the Ebro Basin. Mallos de Riglos, Huesca, Spain.
569
tors as originated by weathering and removal under periglacial envronments.
Mineralogical analyses of the Dartmoor grus make evident the absence of alteration
of feldspars and a low clay content (Doornkamp, 1974). Consequently, in European
latitudes a "sandy weathering product" can form (Bakker, 1967), which can involve
producing blocks.
King (1948) proposed that tors, the same as dome inselbergs, originate by slope retreat
in arid and semiarid climates, giving rise to a pediment at their feet. Similar ideas,
although developed for periglacial environments, were elaborated by Czudek (1964)
(Figure 8.11).
From the above discussion, there is no doubt that there exist several hypothesis for
explaining the origin of such boulders. Two main tendencies can be deduced: one related
to deep weathering and later erosion (the two-stage hypothesis of Linton) and the other
related to slope retreat in warm and cold deserts.
5.2. Domed inselbergs (bornhardts)
As previously noted, the term bornhardt is due to Willis (1936), for defining crystalline
domes in the honour of the German explorer Bornhardt (1900), who first described
inselbergs. They have a dome form and develop on resistant massive rocks, mainly
granites, although also on sandstones and conglomerates in central Australia. Twidale
(1982a) considered the Mallos de Riglos conglomeratic monoliths in the Spanish
Southern External Pyrenean ranges (Figure 21.35), to be bornhardts. This assumption
can be extrapolated to the conglomeratic mountains of Montserrat, Montsant,
Figure 21.35. Monoliths developed on massive horizontal conglomerates in the southern limit of the
external Pyrenean ranges, in contact with the Ebro Basin. Mallos de Riglos, Huesca, Spain.