The major steps in the development of Early Palaeozoic stratigraphy are examined, with special emphasis on early Journal papers by Murchison and Sedgwick, and on their conception of systems and series, which permitted long-distance correlation. Unlike other periods, the Ordovician and Silurian were originally split into series; most stages have only been defined in the past 60 years. From 1880, Lapworth's graptolite zones have allowed much greater chronological precision. More recently, other methods have been developed for recognizing small time divisions, including studies in gradational evolution. A significant new advance is the correlation (by biostratigraphy) of short-lived physical events such as magnetic reversals and sea-level and climatic changes.

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