Caithness Field club Bulletin
April 1975
Deep Weathering of Rock in Caithness
D. Omand
Deep weathering of rocks, thought to be due to the tropical
or sub-tropical climate of the Tertiary, has been widely reported in Scotland
(e.g. Sissons 1967). Caithness is no exception. Here, sites showing deep
chemical weathering or pegmatite and conglomerate (Crampton et alia 1914) and of
sandstone and granite (Fitzpatrick 1963, Smith 1968) have previously been
reported. In the adjacent county of Sutherland pre-glacially weathered gneiss
was recorded by Charlesworth (1955), and Godard (1965) found evidence of old
Terra-Rossa type soils in fissures in the Cambrian limestone reminiscent of
those found in Mediterranean lands.
Personal fieldwork in Caithness led to the recording of
additional sites of deep weathering in sandstone, flagstone, mudstone, granite
and mica-schist. At Altnabreac station(ND003457) the granite had weathered down
to the base of the exposed section, viz. 5m (16ft). Granites and associated rock
types appear to have decayed quite readily to a coarse arkose deposit and impart
to the landscape a smooth outline such as is found in the Knockfin Heights and
in the exhumed land surface of western Caithness where it borders Sutherland.
The fact that the outcrop of Reay diorite occupies a basin is also suggestive of
a history of pre-glacial deep weathering.
Deep weathering in such a diversity of rock types might
indicate that a thick, comminuted regolith (soil mantle) covered the northern
landscape at the outset of the Quaternary, although increasing stream incision
due to the cooler conditions coupled with land uplift in later Tertiary times my
have already begun the removal of some material.
R E F E R E N C E S
CHARLESWORTH, J.K. |
The Late-glacial history of the
Highlands and Island of Scotland. |
Trans. Roy. Soc. Edin. vol. 62
pp. 769-928, 1955. |
FITZPATRICK, E.A. |
Deeply Weathered Rock in
Scotland, its occurrence, age and contribution to soils. |
Journal of Soil Science, Vol.14
PP. 34-43, 1963. |
GODARD, A |
Recherches de geomrphologic en
Ecosse du Nord-ouest. |
Pan's 1965. |
SISSONS, J.B. |
The Evolution of Scotland's
Scenery. |
Oliver and Boyd 1967. |
SMITH, J.S. |
The Evolution of the Moray Firth
Shoreline. |
Unpublished Ph.D. Thesis
University of Aberdeen, 1968. |