British regional geology: Wales

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The British regional geology: Wales has been converted to a series of articles for this wiki. The book is available for purchase at the BGS Online Shop Its full reference is:

Howells, M F. 2007. British regional geology: Wales. Keyworth, Nottingham: British Geological Survey.

British Regional Geology: Wales. Cover image. P749355.



History of geological research
Geotectonic setting

Precambrian and ?Cambrian[edit]

Monian Composite Terrane
Coedana Complex
Blueschist Terrane
Monian Supergroup
Avalon Terrane
South-west Wales and the borders


Comley Series
St David’s Series
Merioneth Series


Ordovician volcanism


Caledonian orogeny


Lower Old Red Sandstone
Upper Old Red Sandstone


Variscan orogeny


Lower Jurassic
Middle Jurassic
Upper Jurassic
Lower Cretaceous
Upper Cretaceous
Oil and gas



Geology and man[edit]

Foreword to the first edition[edit]

Wales has had an influence on the science of geology that is in inverse proportion to its small area. Beneath its land area and adjacent sea are representatives of all the major periods of the stratigraphical column, and some were originally defined here in the 19th and early years of the 20th century. Successive generations of geologists have gathered more and more detail and applied new techniques to achieve our current understanding of the geology.

Since its inception in 1835, the Geological Survey has been mapping and acquiring geological data in Wales. This work has been published as maps, memoirs, sheet explanations and other special publications. In addition there has been a continuous stream of publications, some seminal, from university researchers. This book draws heavily on both sources in order to present an overview of the geology and to draw attention to specific sites of interest.

In the first editions of this British Regional Geology series, Wales was covered by two books — North Wales and South Wales — published in 1935 and 1937 respectively, and there were many later new editions and impressions. The pattern of the geology across the Principality and beneath the adjacent sea bed makes it difficult to maintain presentation of the geology in two volumes about an arbitrary east–west line. The political boundary with England to the east, which loosely approximates to the line of Offa’s Dyke, has been taken as the eastern boundary and the ‘Welsh’ localities (i.e. Lower Palaeozoic) of Shropshire are referred to only briefly. Since the first publications of this series, two main factors have pro- foundly influenced our understanding of the geology; neither was known to the authors of these early books. The first is the theory of plate tectonics, which was formulated through the 1960s largely as a result of the global exploration of the oceans; the second is the data acquired from exploration of the sea floor around Wales in the latter part of the 20th century, by drilling and by geophysical surveys.

The underlying geology is reflected in the contrasting and spectacular features of the Welsh landscape, which attract a multitude of walkers and tourists to the Principality. The easy accessibility from the major conurbations has resulted in the growth of many field centres for natural history studies. We hope that this book will provide a geological overview to students and visitors who are interested in the geology, as well as a summary for the professional geologist, civil engineer and planner.

John N Ludden, PhD, Executive Director British Geological Survey Kingsley Dunham Centre Keyworth Nottingham


This book was written following my retirement from the British Geological Survey, when I was an Honorary Research Associate in the BGS and a Visiting Professor at the University of Liverpool. I acknowledge reviews by Adrian Rushton (Cambrian), Mark Williams and Dick Waters (Silurian), Bill Barclay (Devonian and Carboniferous), Colin Waters and Jerry Davies (Carboniferous), Dave Tappin (Mesozoic), Adrian Humpage (Cainozoic), Dick Merriman (metamorphism); Nick Robbins and Paul Shand provided notes on the hydrogeology. Most pertinently, I am aware of the influence of many colleagues and coworkers, over so many years of working in the Principality, who enthusiastically shared both the problems across this spectacular fragment of British geology and all that fun in considering their possible solution.

Scientific editing on behalf of BGS was done by Stewart Molyneux; the series editor is Audrey Jackson.

Illustrations were produced by the cartographic team lead by Ron Demaine and under the management of Roger Parnaby. Pagesetting was by Amanda Hill.

Photographs are from BGS archive or author’s own (MFH) unless otherwise stated.

Frontispiece This LandsatTM image of Wales and adjacent area is a winter mosaic (Band combination 4, 5, 7). The low angle of the sun shows the physical and some geological features. High ground with sparse vegetation cover is greenish blue in colour, forest is maroon/red and other vegetation is orange; towns and cities show as blue-grey.