Rock cleavage and schistosity

Abstract

Rock cleavage, and here I include schistosity, as a structure by which rocks are fractured or cleaved into thin slices distinct from stratification, appears to have been first recognised by geologists about 1820. It was observed by MacCullach (1819) in the rocks of the Western Isles of Scotland and by Otley (1820, 1823) in the English Lake District. Adam Sedgwick (1835) must be credited with the first truly scientific study of the phenomenon; but more thorough investigations of cleavage and schistosity, and theories of their origin were only seriously started about the middle of the last century. Prominent among the early workers were Beete Jukes (1842), Sharpe (1847, 1849), Darwin (1846), Sorby (1853, 1855, 1856), Laugel (1855), Haughton (1856), Phillips (1856) and Tyndall (1856). The early investigations into the problem were surveyed by Phillips in 1856, and later, when more material was available, by Harker in 1885. E. Cloos (1946, p. 58) considered that: This paper (by Harker) is fundamental...’ The annotated bibliography in the memoir on Lineation by Cloos (1946) contains many valuable references to, and brief summaries of the early papers on rock cleavage. More recently, a most useful pictorial ‘Atlas’ illustrating a wide variety of examples of rock cleavage, collected by Baily, Borradaile and Powell (1977) has been published by the University of Tasmania.