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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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