18 | Great Geologists
Although erroneous in his understanding of the origin
of many rocks, Werner’s global stratigraphy paved the
way for the more detailed stratigraphic thinking of the
19th century.
A principal focus of Neptunism that provoked almost
immediate controversy involved the origin of basalt.
Basalts, particularly those occurring as horizontal sills,
were differentiated from surface lava flows, and the
two were not recognised as the same rock type by
Werner. Lavas and volcanoes of obviously igneous
origin were treated as very recent phenomena,
unrelated to the universal ocean that formed the
majority of layers of the Earth. Werner believed that
volcanoes only occurred in proximity to coal beds
and that lavas were the result of the combustion
of coal. Basalt at high elevations, interbedded with
sedimentary rocks, such as sandstones and shales,
proved to Werner that they were chemical precipitates
of the ocean. Vertical dykes were considered to be
precipitates from the universal ocean infilling fissures.
These views were countered by, amongst others,
the Scottish geologist James Hutton. Hutton
favoured the notion that granites and basalts were
the products of heat within the Earth creating molten
magma (Plutonism). His observation of cross-cutting
intrusions demonstrated this and was a major factor in
the discrediting of Neptunism, along with observations
of modern and ancient volcanoes documented by one
of Werner’s former students, Leopold von Buch.
A second controversy surrounding Neptunism involved
the volumetric problems associated with the existence
of a universal ocean. How could Werner account for
the covering of the entire Earth, and then the shrinking
of the ocean volume, as the primitive and transition
mountains emerged and the secondary and tertiary
deposits were formed? The movement of a significant
volume of water into the Earth’s interior had been
proposed by the classical Greek geographer, Strabo,
but this was not embraced by Werner because
it was associated with conjecture. Nevertheless,
The location of Scheibenberg, as photographed c. 1900. This was a key outcrop in the development of Werner’s
theory of the Earth. The vertically jointed basalts visible on the hill are interbedded with sedimentary rocks and,
in the view of Werner, have gradational contacts. This demonstrated the precipitation of basalt from a universal
ocean, according to Werner.