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Part 2. Lyell and the Development of Geological Science |
School of Earth Sciences, University of Leeds, Leeds LS2 9JT, West Yorkshire, UK
This chapter examines the extensive arguments Lyell brought to bear on the interpretation of sedimentary rocks through the operation of ‘present causes’ in the first Edition of Principles of Geology (1830–1833). A case is made inter alia for Lyell, rather than Sorby, being the true originator of sedimentology and basin analysis, amongst much else of course. Lyell had a special interest in Earth surface processes, and the effects of tectonics and climate on them, because he saw that the evidence is firmly written in the sedimentary products of observable events. His own explanations for the sedimentary and geomorphic processes of erosion and deposition were acutely sensible: he analysed (in today’s parlance) river avulsions, controls on delta morphology, oceanic brine pools, cross stratification, confluence bars, boundary layers, hydraulic geometry, debris flows, sediment budgets, alluvial basin architecture, and clinoforms. Much of Sorby’s work in some of these areas must have been inspired by his reading of the Principles. Lyell was occasionally too much guided by theory, as in the famous sophistry of his 1830 analysis (in the first edition) of the sedimentary and geomorphological evidence for Holocene Fenno-Scandinavian uplift. His willingness in subsequent editions of Principles to abandon such firmly held views in the light of empirical and personally collected field evidence to the contrary presages his momentous decision to throw his weight behind Darwin’s natural selection theories some 30 years later. Lyell was not so rigidly an anti-catastrophist and inductionist as is commonly made out. His writings make very clear his ability to state bold theories. For example, his discussions of climatic change and his concept of the ‘great year’ were outstandingly incisive, holistic and original. They include the role of land-sea interactions, ocean currents and precessional orbital cycles. He even considered the probability that continents and oceans changed position, albeit by vertical movements. The motive for all this came from observations he and others had made on the distribution of Cenozoic molluscs and the need for some general global cooling to explain these. He included in his actualism all manner of extreme (but not ‘catastrophic’) events, for example earthquakes and volcanic eruptions. He was also willing to consider (but then rejected) the possibility of catastrophes, most obviously in his discussion in the seventh edition of Principles (1846) of the possible ‘lake-burst’ of Lake Superior into the headwaters of the Mississippi. One feels he would have welcomed probability theory and the development of magnitude/frequency analysis, and that he would have laughed at any modern description of himself as the ‘father of uniformitarianism’.
