Learning from Leonardo

* Stratigraphy, the branch of geology concerned with the layering, or stratification, of rocks, was pioneered in the seventeenth century by the Danish anatomist and geologist Nicolas Steno (Niels Stensen); see Gohau, A History of Geology, pp. 61ff.

† Sedimentary particles are classified in modern geology according to their sizes and are known, in the order of decreasing size, as gravel, sand, silt, and clay.