Measurement, portrayal and analysis of orientation data and the origins of early modern structural geology (1670–1967)

Abstract

Dip and strike measurements were made by miners as early as 1505 and by the 1770s took place in a ‘geognostical’ context. Early portrayal of dip and strike in maps and the emergence of cross-sections and block-diagrams is discussed. In the 1820s, recordings of cleavage and foliation, lineation, joints, faults and slickensides began. By the 1840s interest in Elie de Beaumont's Systemes de Montagnes encouraged graphical summaries of two-dimensional orientation data (e.g. the strike of bedding, mineral veins or joints). Towards the close of the nineteenth century, primary effort was devoted to regional mapping, resulting in improved understanding of the nature of structures, particularly ‘Alpine’ thrust tectonics. The emergence of Hans Cloos' school of ‘granite tectonics’ in Germany in the 1920s, and its subsequent uptake in the United States, with the emigration of Robert Balk and Ernst Cloos in 1923 and 1930, is noted. Meanwhile, in Austria, Walter Schmidt and Bruno Sander were developing ‘structural petrology,’ dominated by the microscopic analysis of grain-orientation. Its enthusiastic take-up in Europe, Scandinavia and the USA popularized statistical analysis of three-dimensional orientation data. As scepticism grew regarding kinematic interpretations made by structural petrologists, interest in structural analysis based on field mapping returned in the 1940s. The subsequent emergence of early ‘modern’ structural geology in Britain, with its emphasis on statistical analysis of small-scale structures, is discussed. The turning point is placed at about 1952.