Jon Trevelyan (UK)
Just lately, I’ve completed the Nice Silurian Controversy, an impressive e-book in regards to the nineteenth century arguments over the age of the decrease Palaeozoic greywackes/sediments of Devon, and the creation of the idea of the Devonian. And studying The Lewisian: Britain’s oldest rocks by Graham Park, it happens to me that this could maybe be known as, The Nice Lewisian Controversy. It shares the identical historic and scientific intentions, and the identical grand sweep of scientific historical past, this time from the early twentieth century – specifically, the exploration over many years of the geology of the Lewisian of northwest Scotland.
That’s, the e-book covers the early concepts from the 1907 Geological Survey Memoir by Peach, Horne and Geikie (amongst others) to Sutton and Watson’s seminal work of 1951 on the Scourian and the Laxfordian, to the unique mapping of the Outer Hebrides. It then covers the 1960’s re-mapping of the mainland and the Hebrides, with the attendant issues of correlation; and concludes with present fashions and hypotheses, together with the shear zone mannequin, kinematic fashions, Lewisian chronology, and a wider image achieved from trendy tectonic fashions.
One vital level to recollect is that the standard instruments of stratigraphic investigation have been (and are) of no worth in coping with such a fancy assemblage of extremely deformed and metamorphosed rocks. That’s, there is no such thing as a fossil proof and few indicators of recognisable sedimentary strata.
This can be a e-book I believe Dr Graham Park has been wanting to write down all of his educational profession. Graham has studied the Lewisian advanced for over 60 years and is due to this fact in a novel place to offer this account in a scientifically sound however readable method. In truth, he has been a major participant within the historical past of geological investigation of the Lewisian.
The time period “Lewisian” primarily refers back to the ‘Lewisian advanced’, which is a rock sequence uncovered in northwest Scotland, the Outer Hebrides, and notably within the Lewis and Harris areas. It’s now one of the crucial extensively studied Precambrian rock sequences on the planet. It consists primarily of metamorphic rocks, akin to gneisses, which have undergone intense warmth and stress over billions of years. These rocks are usually of Archean age, making them among the many oldest rocks in Europe.
The advanced is known as after the Isle of Lewis, the place the rocks have been first extensively studied. It extends over an enormous space, and includes a various vary of rock varieties, which additionally correlate with historic rock sequences within the east of Greenland.
The Lewisian advanced supplies vital insights into the geological historical past and processes that occurred through the early levels of Earth’s improvement. These rocks have been subjected to a number of tectonic occasions and have skilled folding, faulting and shearing over their long history. Therefore, the bottom line is that the Lewisian complex is significant for geologists studying the evolution of the Earth’s crust and the processes that shaped ancient continents, together with the formation of the geological structures we see today.
I won’t lie – the book is difficult. It has a (very necessary) glossary, but it would be impossible to cover all the necessary scientific words and it doesn’t. Having said that, it is worth struggling with. It is well written but does not shy away from the complex. And it is worth the struggle because, in fact, the first 2.5 million years of the geological history of Britain are stored in the gneisses of the Lewisian Complex; and is therefore important for anyone with an interest in the geology of Britain.
Perhaps I should point out at this stage that one of its complexities is the increasing sophistication of the geochronological and geochemical techniques used to decipher the Lewisian complex. The first important breakthrough was the recognition that a set of intrusive metamorphosed dykes could perhaps be used to separate episodes of deformation and metamorphism that occurred before the dykes were intruded, from those that occurred subsequently. And the science of this is complex.
Much of the extensive literature on the Lewisian is highly specialised and not easily accessible to the general reader. However, this is an attempt to explain the most important and relevant research into a more user-friendly form. It will appeal to many geologists including students, geological visitors to the northwest of Scotland and academics seeking a readable account of remarkable and significant advances in earth science.
Graham Park is Emeritus Professor of Tectonic Geology at the University of Keele and author of the popular Introducing Geology, the title that initiated the successful ‘Introducing’ series, all of which are reviewed in the magazine.
The Lewisian: Britain’s oldest rocks, by Graham Park, Dunedin Academic Press, Edinburgh (2022), 336 pages (hardback), ISBN: 9781780460987.
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