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