Steps in the History of Mudstone Investigations—A Timeline, 1556 Through 2007

In 1556, Agricola published the first detailed description of a mudstone posthumously, but it was not until 1747 that one of them (a black shale) was formally defined by William Hooson. A review of the world literature since Hooson's time shows a slow, steady activity in the study of mudstones in the 1800s, a sharp break to more frequent activity in the early 1920s, a decline during World War II, followed by a return to the pre-war level, but then followed in the 1990s by a possible decrease in activity.

The trends are similar for both conceptual advances and for new techniques. The break in the 1920s was led by new technologies that expanded observations down to the angstrom level with X-ray diffraction and up to the formation scale with down-hole geophysical logging and seismic reflection. A comparison with a similar compilation for igneous and metamorphic rocks shows the same three phases—early slow phase, intermediate rapid phase punctuated by the Second World War, final slower phase—but in the case of the crystalline rocks, the rapid phase begins much earlier, in the 1880s. We suggest that the common techniques of that time—the petrographic microscope and wet chemistry—were well suited to the investigation of crystalline rocks, but the breakthrough for mudstones had to wait for new technologies.