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Figure 2. Maps of the area around the city of Oxford showing the evolution of William Smith’s geological 1770s, Guettard and Lavoisier published a GSA TODAY | www.geosociety.org/gsatoday
mapping and a comparison with the present day geological interpretation simplified from work by the series of mineralogical maps of north-
British Geological Survey. (Extracts of William Smith county maps and the William Smith A map are eastern France showing point locations of
published by kind permission of the Geological Society of London and the P map by kind permission of the rocks and minerals, but no attempt was
Manuscripts and Special Collections, The University of Nottingham.) made to map strata. Later, in 1809, the
Scottish-American William Maclure
(1763–1840) published a geological map
of the United States that pre-dated
Smith’s map by six years. Maclure was
strongly influenced by the work of
Abraham Gottlob Werner (1749–1817),
who had developed a theory of universal
rock genesis based on precipitation and
erosion within a receding primordial
ocean (later known as Neptunism). On
his 1809 map, Maclure used Werner’s rock
classification, which ultimately proved to
be a geological cul-de-sac. Maclure did
meet Smith in 1815 and purchased a copy
of his map, yet he completely failed to
understand the importance of Smith’s
work (Torrens, 2001), for on his 1817
version of the USA map, the classification
is essentially the same as the one he had
used in 1809.

It is not known whether Smith was
aware of Werner’s work, but if so, he was
most certainly not influenced by it. Smith
realized that an understanding of the
“ordering of strata” was essential in
geological mapping, and it was the applica-
tion of his stratigraphic method that was
so geologically significant. Smith first
became interested in this ordering when
employed as a surveyor on the Somerset
Coal Canal in 1795. Through detailed
study of canal sections, he managed to
separate several repetitious clay formations
and also to separate the Upper and Lower
Oolite (Torrens, 2003, p. 161). By August
1797, Smith had made his first attempt at a
more general order of strata, starting with
Number 1 “Chalk Strata” and descending
to Number 28 “Limestone” below the Coal
Measures. In June 1799, at the home of the
Rev. Joseph Townsend, Smith dictated his
famous “Order of the Strata in the Bath
area” to the Rev. Benjamin Richardson
(Phillips, 1844, p. 29) and during the
course of several iterations it evolved into
the geological table, part of which is shown
in Figure 3.

Like others before, Smith could recog-
nize strata based on their lithology, some
rocks (e.g., oolites) being very distinctive.
However the problem with a purely litho-
logical approach to stratigraphy can be the
incorrect correlation of strata of differing
age but with similar lithology. Smith,

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