Stephenson, D., Bevins, R.E., Millward, D., Highton, A.J., Parsons, I., Stone, P. & Wadsworth, W.J. 1999. Caledonian Igneous Rocks of Great Britain. Geological Conservation Review Series No. 17, JNCC, Peterborough, ISBN 1 86107 471 9. The original source material for these web pages has been made available by the JNCC under the Open Government Licence 3.0. Full details in the JNCC Open Data Policy

Allt nan Uamh

[NC 256 179]

Description

A thick sill of a fresh vogesite with a high proportion of large prismatic hornblendes as much as 10 mm long, set in pink feldspar, occurs close to the A837 and can be reached by a maintained path in the beautiful valley of the Allt nan Uamh, best known for its bone-caves. The locality, slightly above the fish-farm, is shown on (Figure 7.16). It has hardened the Salterella Grit which forms an attractive waterfall (Figure 7.17). The sill dips gently to the east and is about 20 m thick. According to Sabine (1953) this is one of the two thickest vogesite sills in Assynt. The other is on the A837 just north of Inchnadamph.

Conclusions

The sill exposed in the Allt nan Uamh GCR site is a readily accessible, coarse-grained example of the most widespread hypabyssal intrusive rock type in Assynt, excellent for teaching purposes as an example of the lamprophyre family.

References