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April 2008

Geology of the Lampeter District - A brief explanation of 1:50,000
Geological Map Sheet 195 (with map)

Lampeter

J R Davies, D I Schofield, T H Sheppard, R A Waters, M Williams &
D Wilson

Published by: The British Geological Survey
Publication date: 2006
ISBN: 978-085272565-8 (explanation); 075183467-X (map)
List price: £18.00 (map and explanation); £12.00 (map); £9.00 (explanation)
34 pp

www.bgs.ac.uk

Fifteen years ago, in stark contrast to the rest of the UK, about a third of Wales was still covered only by mid-19th century Old Series geological maps lacking information on the drift geology. Nowhere was this problem more acute than in the uplands and coast of western mid-Wales. The mapping programme to correct this situation has coincided with much increased user focus on the distribution and geotechnical properties of the superficial deposits, and with the demise of the much respected sheet memoirs deemed over-costly and ‘academic’ in some quarters. Fortunately the splendid ‘finale’ memoir for the mid-Wales transect, published in 1997, provided a detailed background to the stratigraphy and sedimentary facies subsequently mapped in several adjacent map sheets - such as Lampeter, now described in the new format of the sheet explanation.

The bedrock of the Lampeter district comprises basinal and slope apron facies of late Ordovician to early Silurian age, including major turbidite systems laterally constrained by syndepositional topography related to half-graben structures later inverted by Acadian deformation; notably here in the complex faulted core of the Central Wales Syncline (sensu lato, now the Central Wales Lineament). In the east of the map, on a slope rising towards the former basin margin, a new lateral sediment supply route has been recognised, expressed by the late Aeronian to early Telychian Nant Brianne Formation. Beyond this, no major changes to previous tectono-sedimentary concepts in the area have emerged but the new map links up, and provides alternatives in detail, to several previous studies by academic geologists. The relationship of the BGS stratigraphy to that proposed in earlier work might usefully have been included. It is a sign of the times that the potential for hazardous emissions of methane and radon is briefly discussed and geological site conservation gets a mention.

The format of the new maps and explanations has not yet settled down. The Lampeter sheet lacks both magnetic and metamorphic data and is offered only in the bedrock and superficial deposits version; by contrast the adjacent Builth Wells sheet has magnetics but no metamorphic map and is offered in both solid and solid & drift versions. Nonetheless, the new map is another important step towards the completion of modern geological survey in mid-Wales before 2015. The package of map and explanation is very good value for money and an essential tool for all geoscientists and resource planners concerned with the area.

David James, University of Cardiff


Mass Movements in Great Britain
Geological Conservation Review Series, No. 33

R G Cooper (ed)
Published by: Joint Nature Conservation Committee
Publication date: April, 2007
ISBN: 1-86107-481-6
List price: £45.00
348 pp

www.jncc.gov.uk

The Geological Conservation Review began publication in 1986 of a series of well-accepted volumes on British geoscience, reporting important national sites of special scientific interest (SSSI). This latest volume on mass movements was delayed by the untimely death of the main author and has been compiled with additions by a number of contributors and editors.

Following the overall remit of the series, the authors stress that the book follows a minimal approach to site selection by attempting to avoid repetition of similar landslide types in different areas. Whilst this approach is understandable, only 33 sites have been chosen with an obvious bias to inland slope failures in the Scottish Highlands (12 sites) and coastal landslides in southern England (7). This means that areas of England such as Pennines, Cotswolds and South Wales, which have some of the highest densities of landsliding (DoE Landslide Survey; Jones and Lee, 1994), are missed completely from the list.

The first chapter provides a well-structured and informative background, placing the different types of mass movement into spatial and temporal context with good definitions of landslide morphology and mechanisms. It also introduces the structure of the book, which is divided into eight chapters on the basis of bedrock geology, from Precambrian to Pleistocene. This interesting approach shows that all major rock units are represented in the list but only works to a limited degree because of distorted site distribution. Specific reports are well structured and informative and include well-known landslides such as Black Ven, Mam Tor and The Quiraing; plus some esoteric sites such as Lud’s Church (Staffordshire Moorlands) and Buckland’s Windypit (North Yorkshire). The volume maintains the high quality of the series with a good clear layout and excellent diagrams, although many panchromatic photographs lack sufficient contrast.

Given that landslides are important landscape elements, particularly in upland areas of Great Britain, and are an important hazard with social implications, this volume is too prescriptive in its selection of sites. It can be compared to the large number of Quaternary sites published in a series of regional volumes, which contain replicate scientific information. An opportunity has been missed to provide an overall assessment of British mass movements including representative examples from across the country.

Reference: Jones, D.K.C and Lee, M. 1994. Landslides in Great Britain. HMSO, 361pp

Wishart Mitchell, Department of Geography, University of Durham

 

Geology of the Liverpool District - A brief explanation of 1:50,000
Geological Map Sheet 96 (with map)

Liverpool

A S Howard, E Hough, R G Cofts, H J Reeves & D J Evans
Published by: The British Geological Survey
Publication date: 2007
ISBN: 978-085272589-4 (explanation); 0-7518-3404-1 (bedrock folded); 0-7518-3406-8 (bedrock and superficial)
List price: £18.00 (map and explanation); £12.00 (map); £9.00 (explanation)
42 pp

www.bgs.ac.uk

This completely resurveyed pair of 1:50,000 geological maps and accompanying explanation has been published just in time for the City of Liverpool becoming European Capital of Culture. The sheet also covers most of the Wirral peninsula and Dee estuary, plus a significant portion of Flintshire in North Wales to the west. Given that the district has extensive spreads of Quaternary material, one edition shows the underlying bedrock geology in full detail and another a simplified version with the superficial deposits and seabed sediments superimposed on this bedrock.

The Welsh side of the River Dee is quite hilly and the bedrock consists of Carboniferous limestones overlain by mudstones and sandstones including coal measures. In contrast the Wirral and Liverpool areas consist of a thick succession of Permo-Triassic sandstones and mudstones with a more subdued topography. While the superficial geology mainly consists of till and associated glacial and fluvio-glacial deposits, there are spreads of blown sand along the Irish Sea coast and a complex series of coastal zone deposits, including a clearly marked buried channel linked to the River Mersey between Birkenhead and Wallasey. In the offshore areas, apart from till filling the channel near the mouth of the Mersey, seabed sediments are shown along with bathymetric contours (which are mislabeled in places), while the low water mark is undefined. Unlike some BGS maps in this series, tidal levels relative to Ordnance Datum are not stated - this useful information is not quoted or contoured on topographic maps, a significant omission given the range (over 9m) of spring tides in the Mersey. The bedrock edition only shows the extent of offshore faulting and formations in subdued form, and has a second cross-section partly based on gravity and seismic data.

The sheet explanation with colour illustrations is roughly the same A5 size as the folded map, so they pack neatly together in a plastic wallet. The introduction is a clearly written overview with a fine summary map of the bedrock geology, but unfortunately many of the quoted ages are out of date; perhaps most glaring of all it states that the Pleistocene ended 10,000 years ago rather than roughly 11,600. The geological description provides a concise and up-to-date account with key names highlighted in bold along with map symbols for the superficial deposits discussed in the text, which also includes a number of useful tables and clear photographs located with grid references. Following this the applied geology section details the groundwater and mineral resources of the district, along with constraints posed by the geological environment (engineering geology and likely geohazards) on planning and development. It also tabulates ground conditions for the different superficial deposits and bedrock formations. Finally there are details of BGS information sources and an extensive list of up-to-date references.

David Nowell, New Barnet, Hertfordshire