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Figure 3. Composite illustration showing
GSA TODAY | JULY 2016 however, realized early in his career that particular fossils were
associated with each strata. He was an avid collector of fossils, but
unlike the genteel collectors in Bath, did not see them as orna-
ments; to him, they were a key tool to identify and type specific
strata in the geological record, and he built up a huge collection
that he could relate to specific strata. Based on this, it can be fairly He continued the three-dimensional theme in his magnificent
said that he founded the science of biostratigraphy. Some of
Smith’s fossils from his 1816–1819 publication, “Strata Identified
by Organized Fossils…,” are illustrated in Figure 3.
William Smith laid the foundation for stratigraphy in England;
later, his pioneering work was to be continued by others. Of note
were Carl Albert Oppel and Alcide d’Orbigny. Oppel provided a
detailed zonation of the Jurassic by use of ammonites and was able
to subdivide the Jurassic into 33 different zones (Oppel, 1856–1858).
A major revolution in the understanding of stratigraphy came in
the late twentieth century with the advent of high-resolution
seismic acquisition. For the first time it became possible to resolve
individual stratigraphic units and to understand their architec-
ture; from this, the concept of sequence stratigraphy emerged.
Figure 3 includes a diagram of Jurassic sequences, coastal onlap,
and global sea-level change (0 = present day) compared to part of
Smith’s Table of Strata. The science of stratigraphy has made
significance advances during the past 200 years, yet for all these
advances there is still a direct link back to William Smith’s
original work.
STRATIGRAPHY IN THREE DIMENSIONS
Smith’s interest in representing geology in three dimensions
can be traced back to his early career as a mine surveyor. In 1793,
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part of William Smith’s geological table
of strata, some examples by Sowerby of
stratigraphically arranged fossils from
Smith’s 1816–1819 publication, “Strata
Identified by Organized Fossils…,” and a
modern stratigraphic sequence chart of
the Jurassic (modified from Snedden and
Liu, 2010).
he proposed to make a reduced scale model of the Mearns
colliery showing the coals and other strata (Phillips, 1844, p. 6).
Later, Smith made a geological model by taking one of his
geological maps and cutting along the edges of the strata in
order to accentuate their relationships (Phillips, 1844, p. 27).
stratigraphic cross sections. From 1817 on, he prepared and
published a series of seven cross sections across England and
Wales. Smith did not invent the geological cross section, for it is
known that he was influenced by the pioneering work of John
Strachey (Strachey, 1727, Fuller, 2004, p. 15). However, Smith
took sections to a new level by combining a two-dimensional
cross section with a three-dimensional panorama. Using
modern digital technology, it is possible to further enhance
these sections. The display in Figure 4 shows Smith’s section
across the Weald of southern England, together with part of his
1815 map, which has been draped on a digital elevation model.
Also shown is a modern composite seismic section (Butler and
Jamieson, 2013). Smith’s cross section demonstrates the general
anticlinal structure of the Weald with the chalk dipping to the
north and the south. However, he wrongly interpreted the age of
the thick section in the core of the anticline as Jurassic (Smith
Strata Numbers 8–13). This was understandable because he had
never before encountered thick strata between the Greensand-
Gault and Portland-Purbeck stone. For obvious reasons, he
could not have known that the Weald had been an actively
subsiding basin during the Mesozoic, which had subsequently
been inverted and unroofed. For all this, the cross section
remains a remarkable achievement.