Aka “Strata Smith”.
On the 5th of January, 1796, while on a fact-finding mission to survey routes for a planned, double-branched, Somerset coal canal, which was intended to take land-locked coal to the sea and, via other canals, to London, Smith “recorded his critical observation that some of the strata contained fossils, and those that did could be identified by them. This realization allowed Smith to separate, for the first time, strata which had previously been confused because of a shared lithology. This was a major geological breakthrough. Further, Smith’s training as a surveyor led him to realize that he could colour such strata onto maps, since he understood their thickness and dip and thus their geometry. From 1799 he started both to map local strata and to show them on geological cross-sections” (Torrens for DNB online).
The economic impact of Smith’s ideas was enormous. For the first time the presence of coal, iron, clay, and other minerals so vital to an industrialized Britain could be more accurately determined. At successive premises in Bath and London, Smith displayed characteristic fossils on shelves in accordance with where they had been found in the various geological strata of England.
Soon Smith came to the attention of the president of the Royal Society, Sir Joseph Banks, who opened a subscription towards publication of Smith’s intended Geological Map. Eventually, in 1812 John Cary offered to publish it, the first version appearing in August of 1815, with modifications to about 1818. In May of 1819 the first in a series of geological county maps were issued. Unfortunately, it was all a bit too late, and Smith was in serious financial trouble. In June of 1819 he was imprisoned for debt. At Banks’s suggestion the British Museum acquired Smith’s fossil collection, and his library and personal papers were sold.