"And through all of this, in mine after mine, in quarry after quarry, what was perhaps the most crucial realization of all in this time of early, primitive discovery -- the fact that recognizable seams of coal would always be in the same position compared to one another. The Dungy Drift -- identifiable by its thickness, its color, and its fauna and flora -- was always above the Perrink.... Never once -- unless the Variscan folding has turned the whole bedding upside down, and a skilled observer could always tell if a rock bed was the right way up or not -- would the Slyving be anywhere than above the Great Course and the Firestone." (The Map That Changed the World, page 72)
Coal was very important to England at this time. Not only did it provide heat to homes and businesses, it was also necessary for the fledgling Industrial Revolution. Property owners across the country hoped that coal might be found on their land and insure their coming wealth. Due to his realization of how the order of rock types lay in the region surrounding Bath, Smith became famous for his ability to predict, without fail, whether coal would be found on a property, merely by surveying the type of rocks on the surface. When his employers planned to dig a canal to transport the coal produced in Somerset to the nearby city of Bath, Smith's knowledge of geology (The word was first used in its modern sense in 1735, but the concept could not really be considered mature until 1795. "Geology" did not even appear in the Encyclopedia Britannica until its Fourth Edition in 1810.) made him the obvious choice to survey the land and choose a route for the canal.
For years, Smith had pondered how he might produce a map that would show the geology of the area around Bath that he had surveyed so thoroughly. In 1798 he came across a small map showing the various soils and types of vegetation found in the countryside around Bath, published in the Somerset County Agricultural Report. This map was hand-colored to differentiate the various features. Smith suddenly realized that he could use color to differentiate various types of rocks. In the summer of 1799, Smith produced a circular map entitled "A Map of Five Miles round the city of Bath." Painstakingly hand-colored, the map showed only a limited area and showed the outcrop of only three types of rock, but it was the first geological map and set the stage for future geological maps. (In 1831 Smith presented a copy of this map to the Geological Society of London in Piccadilly, where it resides today.)
