67. Dalradian of Scotland (2009)
The Dalradian of Scotland probably offers the greatest variety of metamorphic rocks to be found in the British Isles. Here we find sedimentary rocks originally ranging in composition from muds to sandstones and conglomerates as well as a wide range of calcareous rocks and volcanics.
The ‘Boulder Bed’, of glacial origin, is perhaps the most spectacular and interesting of all these rocks. Sedimentary structures are beautifully preserved providing evidence of depositional environments progressing from fluvial to oceanic. A complete range of metamorphic conditions has affected these rocks, giving rise to slates, phyllites and schists, together with quartzites, gneisses, amphibolites and marbles. The range of pressure and temperature conditions that the rocks were subjected to has induced the growth of porphyroblasts of chlorite, biotite, garnet, staurolite, kyanite and sillimanite; the area provided the earliest descriptions of the conditions of the growth of metamorphic minerals and their relationship to the structural history.
It is the detail of this structural history that is the main focus of the book. Folds of several generations and scales are spectacularly exposed and provide unrivalled examples of refolding, the imposition of one generation on another.
The description of these features is made by reference to three traverses across the Dalradian, in the southwest, the centre and the northeast. These three are based on major routes but the exposures are generally reached via quiet minor roads. As well as roadside cuttings, they involve sections in small streams and on low hillsides; in the southwest and northeast they are mostly on pleasant coastal sections. The 202-page guidebook includes 76 mostly full colour figures and photographs, the geological context, general descriptions of the lithostratigraphy, structure and metamorphism, a glossary of geological terms and a comprehensive reference list for further reading.
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