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Geoscientist Online

Logging the Chalk

Mortimore

There is a lot more to chalk than the White Cliffs of Dover, and this book does an excellent job of describing the huge variety of lithologies and fabrics which this material hosts. The emphasis here is on the English Upper Cretaceous, but since this material is encountered in many civil engineering projects and across the North Sea it is likely that all engineering geologists and geotechnical engineers will encounter it at some stage of their professional career. When they do, this is the book to have to hand.

The author commences with a concise account of the stratigraphy, which no longer features “Upper”, “Middle” and “Lower” but instead uses a new set of terms which better reflects the regional variations. The bulk of the book is then devoted to the recognition and description of chalk within the four main provinces: Southern, Transitional (London, Chilterns and East Anglia), Northern, and Central Graben (including the Northern North Sea). However, there is hardly any text!  The majority of the pages are devoted to a wonderful array of annotated photographs which reveal the extent and variability of chalk and its component lithologies and fabrics. Particular attention is paid to weaknesses and heterogeneities which might otherwise have been overlooked, to the detriment of the engineering project concerned.

Adequately describing chalk for engineering purposes has always been difficult given its tendency to break up during drilling and its sensitivity to changes in moisture content. Nevertheless the degree of deterioration brought about by natural weathering is of considerable geotechnical importance and the author provides a pragmatic approach to its description and assessment. This is of particular help when attempting to interpolate between boreholes and/or exposures. The final 20% of the book is devoted to the description of chalk logs.

One of the beauties of this book is the wonderful set of coloured photographs used to portray chalk profiles. The high quality of reproduction more than justifies the high cost of publication. The publisher has also made available a pdf copy of three additional appendices covering typical chalk core logs through a variety of weathered profiles, logs of cable tool percussion samples, and the impact of sonic drilling on penetrating chalk profiles.

The other beauty is the author’s masterly synthesis of chalk description built up over nearly half a century of study based on the seminal work of BRE (the Mundford scheme by Ward, Burland & Gallois), SML (Spink & Norbury) and CIRIA using his own extensive experience of chalk encountered in a wide range of engineering projects and field settings.

The profession can only hope that this will become the template for a whole host of similar volumes covering the geological units with which they have to deal: Mercia Mudstone, London Clay, Sherwood Sandstone, . . .

LOGGING THE CHALK by Rory N. Mortimore, 2014. Published by: Whittles Publishing 352 pp (hbk) ISBN: 978 1 849 95098 5  List price: £135.00

Reviewed by Mike Rosenbaum