The geology of the Mendip Hills of southwest England is familiar to many British geologists, although most will never have set foot in the area. Our knowledge comes from either the Wells 1:50,000 map or from the Bristol 1:50,000 special sheet, both classic maps for teaching and learning geological map interpretation in the UK. In the Mendips, the Devonian to Carboniferous succession was thrust and folded by the Variscan (late Carboniferous) shortening and then eroded at the arid Permian land surface. The delicately sculpted landscape of wadis and interfluves was then preserved beneath onlapping Triassic and Jurassic deposits, before being exhumed during Palaeogene and Neogene uplifts. The Quaternary river and estuarine deposits of the Somerset Levels to the south now enhance a strong scenic contrast with the more resistant uplands of the Mendips.
Why do relatively few geologists venture to visit this, on paper, classic terrain? Probably because, being south of the Quaternary ice limit, the degree of natural rock exposure in the Mendips is less than in glaciated areas further north. Students are taken, for instance, to the Yorkshire Dales to see Carboniferous rocks, or to the south Pembrokeshire coast to see their Variscan deformation. Publication of Andy Farrant's two map and guide sets to Mendip geology is an attempt to increase the popularity of this underused area.
The format of these guides is genuinely innovative, and conspicuously successful. Usually, geological itineraries in guidebooks are keyed to localities numbered on page-size line figures, only sometimes summarising the geology as well as topography. The localities in the Mendip guides are shown instead on two purpose-drawn full-colour 1:25,000 geological maps. This format allows each itinerary to be studied in its regional context. Crucially, contours, roads and other topographic components are clear enough to be used for navigation, and rights of way are emphasized in green. Gone then is the need to juggle all three media usually required for geological tourism: guidebook, geological map, and topographic map. Each main map mostly depicts bedrock geology, with only large areas of superficial deposits. Each map sheet also includes inset maps of local detail at 1:20,000, shaded relief and simplified bedrock geology maps at 1:100,000, four cross-sections, and a key.
Each booklet begins with sections on the rock types, the glacial history and the economic geology. Eleven or twelve local itineraries follow, each providing about half to one day's enjoyment. There is a geological glossary, some information on transport links and tourist offices, and good list of further reading and websites. Indeed, there is a ‘Foundations of the Mendips’ website, hosted by the British Geological Survey, which includes some of the book material and much useful information besides. The acknowledgements are notable for the wealth of acronyms. The project used funding from the SAMP, funded through DEFRA as part of the ALSF administered by MIRO for the DCLG. Whatever; the price has been held to a very reasonable £12 for each guide-plus-map package.
I have almost nothing but praise for these excellent publications. The booklets are written at a well-judged level accessible to the novice geologist yet rigorous enough to be useful to the professional. The illustrations are colourful and informative. The maps are a pleasure to use. My only quibble is with the unnecessary vertical exaggeration on the map and booklet cross-sections: Variscan structures are impressive enough and better understood without this ‘enhancement’. However, this is no reason for potential visitors to the Mendips not to buy both these sets and to make better geological use of this important area.
