Great Geologists | 59
Dana’s Geosynclinal Theory
in the expedition’s Report on Geology, a landmark American
geological publication that took thirteen years to complete. In
another parallel with Darwin, this report included a discussion of
how coral reefs form around volcanic islands. Dana included ideas
omitted by Darwin; for example, that atolls may become deeply
submerged as a result of subsidence — “guyots” in today’s
terminology.
In this report and associated papers, Dana produced the first
description of many key geological localities. One was Mount
Shasta on the California coast. His description of the geology
of this area contributed to the California Gold Rush after he had
mentioned the likelihood of finding gold deposits in the region.
The contrast between the geology of the Andes and the Pacific
Ocean led Dana to consider the continents and ocean basins as
separate, permanent and geologically distinct. Arc volcanoes and
active mountain belts bound the inactive continental interiors
as a result of a cooling, contracting globe. The ocean basins are
where volcanic material has vented to the surface and is resisting
contraction. Although these ideas are now, in the light of plate
tectonics, fundamentally incorrect, they do contain grains of truth
that support the notion of a dynamic Earth. For example, Dana’s
description of linear volcanic island chains in the Pacific led to
the hypothesis of Tuzo Wilson that plates pass over hot spots,
producing linear island chains in their wake. Plate tectonics has
confirmed the contrast in age and structure between continents
and ocean basins, and involved the distinctive character of ocean
basins, as emphasized by Dana, into the modern global synthesis.
As a result of his thinking on global geology, Dana was engaged
in a debate that dominated much of American geoscience in
the second half of the 19 th century, namely, the processes by
which mountains form. The essence of this was the geosynclinal
theory, which arose out of a vigorous debate between Dana and
the New York geologist, James Hall. Geosynclinal theory can be
divided into two main stages. First, large quantities of sediment