Great Geologists | 17
Natural History at Edinburgh (and, in turn, taught Charles
Darwin) and Alexander von Humboldt, one of the true
greats of Natural History in the early 19th century.
Jameson would become amongst the most vocal and
articulate promoters of Werner’s ideas.
Werner emphasised to his students the importance of
making accurate geological observations in the field.
According to Werner, rock units or “formations” (Gebirge:
literally, mountains) had three dimensions (i.e. structural
relationships to each other and to the topography, as well
as a distinct stratigraphic order). In his geological thinking,
Werner was much influenced by the publications of his
fellow countryman, Johann Gottlob Lehmann. Lehmann
had built on the Law of Superposition, as earlier described
by Nicolas Steno, and emphasised the importance of
layering within rock successions — what we now term
“stratigraphy.” Whilst Lehmann described stratigraphy on a
local scale, Werner expanded these ideas to a global scale.
Werner proposed new ways of thinking about geologic
formations, redefining formation to refer not just to the
chemical and lithological makeup of a rock, but to the
timing of its development. He defined formations as
“bodies of rock laid down in the same period,” giving
scientists a new way of thinking about geological history.
These ideas were first published in a booklet in 1787 —
Kurze Klassifikation und Beschreibung der verschiedenen
Gebirgsarten (Brief Classification and Description of the
Different Species of Formations).
By 1796, Werner believed that the stratigraphy of the
Earth could be divided into five principal formations,
mostly related to deposition within, or precipitation from, a
primordial ocean:
1.
Primitive (Urgebirge) Formation: granites, gneiss,
schists and metasediments considered to be the
first precipitates from the ocean
2. Transition (Übergangsgebirge) Formation:
limestones, dykes, sills and thick sequences of
greywackes with few or no fossils that were the
first orderly deposits from the ocean
3. Secondary or Stratified (Flötz Gebirge) Formation:
the remaining, obviously stratified and clearly
fossiliferous, rocks. These were thought to
represent the emergence of mountains from
beneath the ocean and were formed from the
resulting products of erosion deposited on their
flanks.
4. Alluvial or Tertiary (Aufgeschwemmte Gebirge)
Formation: poorly consolidated sands, gravels
and clays formed by the withdrawal of the ocean
from the continents
5. Volcanic (Vulkanische Gebirge) Formation:
younger lava flows demonstrably associated with
volcanic vents. Werner believed that these rocks
reflected the local effects of coal combustion.
These five units were divided into a variety of sub-units,
based on Werner’s observations around Saxony. He is
often criticised for developing a global stratigraphy from
observations within only a small area of central Europe.
However, it can be noted that he was an avid collector of
geological literature and must have found support for his
ideas in such readings.
The basic concept of Wernerian geology was the belief
in an all-encompassing ocean that gradually receded
to its present location, while precipitating or depositing
almost all the rocks and minerals in the Earth’s crust. The
emphasis on this initially universal ocean spawned the
term Neptunism, which became virtually synonymous
with Wernerian teaching. A universal ocean led directly
to the idea of universal formations, which Werner
believed could be recognised on the basis of lithology and
superposition. He used the term “geognosy” (meaning,
knowledge of the Earth) to define a science based on the
recognition of the order, position and relationship of the
layers forming the Earth. As he commented towards the
end of his life, “Our Earth is a child of time and has been
built up gradually.”
The notion that most rocks are the result of deposition in
a primordial ocean is patently wrong. However, Werner’s
ideas can, nonetheless, be translated into aspects of
the geological history of the Earth and its associated
stratigraphy that we know today. His Primitive and
Transitional Formations may represent Precambrian
basement and sediments, respectively, whilst his
fossiliferous Secondary (Flötz) Formation may represent
much of Phanerozoic sedimentation. His Alluvial and
Volcanic formations represent relatively recent rocks.