The Lewisian: Britain’s Oldest Rocks
There is a particular interest in old rocks: whether they record different geological processes to the present and whether we can approach them in similar ways to younger rocks. Britain’s oldest rocks, the Lewisian, are excellently exposed in the northwest corner of Scotland. They have been studied for two centuries and have often been at the forefront of debates about early Earth history. Park has been actively researching the Lewisian for over 60 years and, using his experience, this book reviews the progression of ideas on the Lewisian since the early nineteenth century.
The book addresses the early pioneers of Lewisian geology, data collection methods, and the development of models, which were, in turn, tested against the geological record. It covers many different areas of geology, from the role of igneous events, such as the Scourie dykes, in establishing the relative ages of different episodes, to the effect of the quantification of structural analysis in the 1950s. The application of geochemistry in constraining whether Laxfordian gneisses represented metasediments or a volcanic origin, and early analyses of Rare Earth Element patterns in gneisses are examined. A long-standing debate over the origin of layering in gneissic terranes being primary or the product of deformation is also detailed.
Radiometric dating revolutionised Earth science and it had a critical role in studies of the Lewisian, from the development of Ar dating in the 1950s, through to increasingly precise Pb-Pb and U-Pb geochronology. The final chapters provide a useful review of the present state of geochronology in the Lewisian and the advances in palaeomagnetism that allowed the Lewisian of northwest Scotland to be linked with other fragments of ancient crust.
The Lewisian remains a classic area that provides a record of the evolution from granite-greenstone terranes to assemblages consistent with crustal thickening and plate tectonic processes. It has been influential in the development of ideas about Archaean geology, and fully warrants this history of the people, ideas, and controversies involved in Lewisian geology. The author is to be congratulated on his sure handling of these debates and discussions. The book is excellently presented, with a good balance of field photographs and clear and accessible diagrams. It is a welcome contribution for those interested in the development of ideas in Archaean geology and the part played by the rocks of northwest Scotland over the last 200 years.
Reviewed by Chris Hawkesworth
BY: G. Park (2022). Dunedin Academic Press. 336 pp. (hbk)
PRICE: £40.00 www.dunedinacademicpress.co.uk