29/4/2013

EARLY GEOLOGICAL MAPS a talk by DUNCAN HAWLEY

There was unusual interest in the April evening meeting when Duncan Hawley, from Swansea Metropolitan University, spoke on Early Geological Maps. He also brought along a splendid selection from his own collection. ‘The geological map is the dynamic force in geology, and the history of its evolution and development is the history of the birth and growth of geology’, so said FJ North in 1928, when he was the first keeper of geology at the National Museum of Wales.

Packe, in 1743, used hatching to depict the topography of Kent, probably the first geomorphological map. Early maps were monochrome; some, like Wm Maton, in 1793, believing that colour would be a distraction. By early 1800s colour became widely used, as in Gimbernat’s map of the Tyrol. In 1809 Jamieson produced the first guide ‘on colouring geognostical maps’. The earliest maps merely noted spot descriptions of rock and correlation over long distances began with Guettard’s 1746 map of France and southern Britain, an early mineral map which picked out the chalk on both sides of the Channel, but depiction of continuous boundaries was common by mid 19th century. Guides on mapping geology were introduced in the 19th cent, for example Henry de la Beche’s Geological Manual (1831) and Ami BouĂ©’s Guide du Geologue Voyageur.

Early geological cartographers frequently worked alone, a serious disadvantage, resulting in considerable inaccuracy. Wm Smith first attempted to delineate geological strata in 1801. His 1815 map is a magnificent one-man effort, with about 100 of the 400 printed copies still surviving. But the collaborative efforts of men like George Bellas Greenough achieved more, by compiling the work of local experts like Fitton, Buckland and Aikin. That effort, through the young Geological Society of London, was in fact already mostly completed by 1812, though not published until 1819. The earliest mappers even had to work without ordnance survey maps. Even with basic maps the geological contours were often inaccurate, changing markedly within a few years, as shown by comparing Murchison’s map of Wales and the borders in 1839 with that of the Geological Survey only six years later.

Colour posed a problem for early geological map publishers, first being added to individual copies by hand, often by young women, thought to be more skilled in that work; though hand colouring also sometimes led to inaccuracy, and darker colours could obscure the underlying information. Smith’s map used gradational colouring to show strata becoming younger, and Farey in the 1810s showed how structural features like faults can be interpreted using colour to show the outcrop patterns they produce. However, by the mid-1800s printed colour maps began to emerge and was cheaper but less accurate and more technically difficult to produce until the 1880s when printing became inevitable as more detail was added to maps. Today’s mapping is done with the geological equivalent of an iPad and the modern maps are things of beauty. What would the early workers have thought. The audience was much taken with Duncan’s evident enthusiasm for his subject, and a vote of thanks was proposed by Tony Thorp.

Next Indoor meeting: Wednesday 15th May

Two ½ hour talks: