The essentially E–W-trending structural grain of the Devonian and Carboniferous Variscan orogen of mainland SW England (see Chapter 10) is punctuated by five large granite plutons (Fig. 11.1), which are now known to have been emplaced during very latest Carboniferous–Early Permian times. This chronological frame is after the final compressional stage of the Variscan orogeny, and it is now considered that the Cornubian granites were associated with crustal extension and orogenic collapse – this is discussed more fully later. From east to west the plutons are: Dartmoor (650 km2), Bodmin Moor (220 km2), St Austell (85 km2), Carnmenellis (135 km2) and Land’s End (190 km2). Offshore, to the west of Land’s End, the Isles of Scilly pluton has a seabed crop of about 120 km2 . Onshore, there are a number of smaller granite bodies, including Hemerdon Ball (south of Dartmoor), Hingston Down, Kit Hill and Gunnislake (between Dartmoor and Bodmin Moor), Belowda and Castle-an-Dinas (to the north of St Austell), Carn Brea, Carn Marth, St Agnes and Cligga Head (to the north of Carnmenellis), St Michael’s Mount and Tregonning–Godolphin (between Carnmenellis and Land’s End).
The higher parts of the granite outcrops are characterized by moorland, with thin peaty soils from which arise sporadic tors and their associated boulder screes, ‘clitter’ in the local dialect.
Figures & Tables
The Geology of England and Wales
This second edition of The Geology of England and Wales is considerably expanded from its predecessor, reflecting the increase in our knowledge of the region, and particularly of the offshore areas. Forty specialists have contributed to 18 chapters, which cover a time range from 700 million years ago to 200 million years into the future. A new format places all the chapters in approximately temporal order. Both offshore and economic geology now form an integral part of appropriate chapters.
Most of England and Wales is formed from part of a single terrane, Avalonia, and its pre-Cambrian (Neoproterozoic) history is preserved in patches. However the time intervals from the Cambrian to the present day are well represented in our sequences and the Cambrian, Ordovician, Silurian and Devonian systems were all defined here. William Smith's map of England and Wales was the world's first geological map of a country and the British Geological Survey's copy is reproduced in the introductory chapter. This chapter, by the editors, consists of a broad overview aimed particularly at the non-specialist while guiding the reader towards the appropriate succeeding chapters. The volume concludes with a look at the future, from the short-term effects of climate change and sea-level rise to the position of our region in a possible plate tectonic configuration 200 million years hence.
While the authors have taken a ‘dynamic’ view of the evolution of the area over geological time, they have also ensured that the geological evidence on which the interpretations are based is reviewed thoroughly. Hence the volume provides a valuable resource for both Earth scientists and the broader community.