Figure 2.1   (a) Steno’s series of diagrams illustrating the deposition of strata, their erosion and subsequent collapse (25, 24 and 23) followed by deposition of further successions (22, 21 and 20). These diagrams demonstrate not only superposition but also the concept of unconformity. (b) Giovanni Arduino’s primary, secondary and tertiary systems, fi rst described from the Apennines of northern Italy in 1760. These divisions were built on the basis of Steno’s Law of Superposition of Strata. (c) Idealized sketch of William Smith’s geological traverse from London to Wales; this traverse formed the template for the fi rst geological map of England and Wales. Data assembled during this horse-back survey were instrumental in the formulation of the Law of Correlation by Fossils. (a, from Steno 1669; c, based on Sheppard, T. 1917. Proc. Yorks. Geol. Soc. 19.)

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