TRAVELOGUE OF SCOTLAND: VENERABLE OUTCROPS AND THE VISIONARY GEOLOGISTS WHO STUDIED THEM

If James Hutton is considered the father of modern geology, Scotland is its birthplace. The concepts of deep time, igneous rocks, crosscutting relationships, depositional environments, and thrust faults sprang from the 18^th and 19^th Century Scottish Enlightenment. These ideas challenged and changed prevailing worldviews; the rugged landscape provided evidence. This talk is a travelogue of some of the famous localities associated with these concepts.

Hutton’s Theory of Earth proposed cycles of uplift, erosion, and submergence driven by heat from Earth’s interior. His discovery of intrusions at Glen Tilt and Salisbury Crags supported arguments for an igneous origin of crystalline rocks. In 1788, Hutton, John Playfair, and James Hall sailed the coast of East Lothian and Berwickshire to test Hutton’s idea of deep time. They landed on a rocky beach at Siccar Point and discovered an angular unconformity between graywackes and the overlying Old Red Sandstone. While the outcrops demonstrated compelling evidence for deep time, it took publication of Playfair’s Illustrations of the Huttonian Theory of the Earth and Lyell’s Principles of Geology for the ideas to take hold.

In 1841, Hugh Miller, stonemason, paleontologist, writer, and editor made the science of geology even more accessible to the public. He wrote articles for the Examiner and from these, compiled The Old Red Sandstone. Miller’s passion for the Old Red Sandstone came from tracing it over much of Scotland describing fossil fish from Cromarty. He recognized they were unlike living representatives.

The Scottish geologist Roderick Murchison, who named the Silurian and Permian systems, was associated with two controversies that ultimately advanced new concepts. The Cambrian-Silurian boundary dispute was resolved with the compromise proposal of an Ordovician system by Charles Lapworth. The Highland controversy took decades to unravel and was a paradigm shift: rocks are not always found in situ. Publication of The Geologic Structure of the North-West Highlands of Scotland in 1907 highlighted work of Ben Peach and John Horne at Knochan Crag, where they identified and described the first known thrust fault; it placed Precambrian Moine Schist over a lower Paleozoic succession. These outcrops were instrumental in developing some of the earliest ideas of our science.