60 | Great Geologists
are deposited within a down-warped part of the crust. Second,
these sediments are folded within the mountain building process.
Dana described the crustal down-warp area as the “geosynclinal
region,” and the product of the whole process as the “mountain
chain-synclinorium.” Dana also emphasized that the trend of
the mountain range follows the deepest part of the geosynclinal
trough.
There were a handful of suggested hypotheses to support the
mechanism of geosynclinal theory. Dana preferred to rely on that
of a contracting Earth. Compressional, lateral forces were thought
to crinkle up the geosynclinal sediment troughs to produce
mountain ranges. James Hall supported what was known as the
gravitational sliding hypothesis. This hypothesis relied on isostatic
upwarping of geosynclines, paired with the slipping of strata
over basement rocks along a flat shear surface. No matter the
mechanism, it is important to note that they all embraced purely
lateral crustal movement, a concept that would be overtaken by
the work of Eduard Suess and other Europeans studying the Alps.
Dana spent his entire academic career at Yale until his death in
1895. During that time, he was a prodigious publisher in the field
of geoscience, including seminal textbooks, such as his Manual
of Mineralogy and his Manual of Geology first published in 1863.
He also published Corals and Coral Islands and Characteristics
of Volcanoes, the latter completed after a return to Hawaii when
he was in his seventies. His legacy was continued by his son,
Edward Dana, a noted mineralogist in his own right. Although
Dana’s name is now mainly associated with his mineralogical
studies and textbooks, he was the first American geologist to
emphasize the global nature of geology and develop theories to
explain the presence of mountains and oceans. These concepts
may be outdated now, but they helped set geological science
on the path to the plate tectonic paradigm that governs geology
today.
REFERENCES
This essay has drawn upon information from the following
sources:
Gilman, D.C. 1899. The Life of James Dwight Dana. Harper &
Brothers Publishers.
Greene, M.T. 1982. Geology in the Nineteenth Century. Cornell
University Press. 324pp
Natland, J.H. 2003. James Dwight Dana (1813-1895):
Mineralogist, Zoologist, Geologist, Explorer. GSA Today, February
2003, 20-21.
Oldroyd, D.R. 1996. Thinking About the Earth. Athlone.
Oreskes, N. 1999. The Rejection of Continental Drift. Oxford
University Press. 420pp.
https://publish.illinois.edu/platetectonics/geosynclinal-theory/
Part of the mineral collection of Yale University is now housed in the David Friend Hall of the university’s
Peabody Museum. The collection was initiated by Dana and his mentor Benjamin Siliman.