ABSTRACT. The old global tectonics of James Dwight Dana was one
of America's first major contributions to theoretical geology.
That theory began with Dana's experiences in the Pacific on the
Wilkes Exploring Expedition (1838-1842), which paralleled closely
the experiences of Charles Darwin a few years earlier. He refined
Darwin's hypothesis of oceanic subsidence in 1843 by adding geomorphic
evidence of subsidence, differential crustal responses, and variable
island ages, and went on to develop a comprehensive global theory
during the remainder of his life. Dana accepted the long-standing
assumption that the Earth began molten and had contracted as it
cooled. Early in his career, he recognized the fundamental geologic
difference between continents and ocean basins, which he believed
had arisen early in the history of the planet. He inferred that
the northwest and northeast trends of many linear island chains,
shorelines, and mountain ranges reflected fundamental cleavage
lines, which he thought had originated during Archean thermal
contraction and continued to influence subsequent evolution of
the crust. Because continents "were first free from eruptive
fires," they must have cooled first and, being very old,
must also be permanent. With their active volcanoes and depressed
topography, ocean basins must be the chief loci of cooling and
contraction. Furthermore, their greater subsidence inevitably
causes lateral pressure, folding, and uplift of continental margins
to form mountains.
The geosyncline was a late refinement from 1873 in response
to Hall's 1857-1859 "theory of mountains with the mountains
left out" (according to Dana). Contractive pressure buckled
the continental margin; a downbuckle or geosynclinal received
thick sediment derived by erosion of a complementary unbuckle
or geanticlinal. Finally, the whole system failed and became
stabilized as an addition to the growing continent while a new
geosyncline-geanticline couplet formed oceanward. Dana regarded
North America as the perfect, simple example of continental evolution,
which "revealed God's plan of creation" better than
any other continent, therefore it could instruct the rest of the
world. Its margins reflect the northwest and northeast cleavage
lines with the oldest Azoic rocks representing the "first
germinant spot" or nucleus around which the continent had
expanded by additions of mountain belts through successive "vibrations
of the crust." Thus was born the important concept of continental
accession or accretion with "contraction as the power,
under Divine direction, for humanizing the earth." Dana's
old global tectonics had profound influence even after thermal
contraction lost favor around 1910. First Chamberlin's gravitational
contraction and later thermal convection extended that influence
and helped nurture the American resistance to continental drift
until the new tectonics appeared in the 1960s.