DANA,JAMES,DWIGHT OLD TECTONICS - GLOBAL CONTRACTION UNDER DIVINE DIRECTION

The old global tectonics of James Dwight Dana was one of America's fir st 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 subsid ence 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 ac cepted the long-standing assumption that the Earth began molten and ha d contracted as it cooled. Early in his career, he recognized the fund amental geologic difference between continents and ocean basins, which he believed had arisen early in the history of the planet. He inferre d 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 a nd continued to influence subsequent evolution of the crust. Because c ontinents ''were first free from eruptive fires,'' they must have cool ed first and, being very old, must also be permanent With their active volcanoes and depressed topography, ocean basins must be the chief lo ci of cooling and contraction. Furthermore, their greater subsidence i nevitably 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 mo untains left out'' (according to Dana). Contractive pressure buckled t he continental margin; a downbuckle or geosynclinal received thick sed iment derived by erosion of a complementary upbuckle or genaticlinal. Finally, the whole system failed and became stabilized as an addition to the growing continent while a new geosyncline-geanticline couplet f ormed oceanward Dana regarded North America as the perfect, simple exa mple of continental evolution, which ''revealed God's plan of creation '' better than any other continent, therefore it could instruct the re st of the world. Its margins reflect the northwest and northeast cleav age lines with the oldest Azoic rocks representing the ''first germina nt spot'' or nucleus around which the continent had expanded by additi ons of mountain belts through successive ''vibrations of the crust.'' Thus was born the important concept of continental accession or accret ion with ''contraction as the power, under Divine direction, for human izing the earth.'' Dana's old global tectonics had profound influence even after thermal contraction lost favor around 1910. First Chamberli n's gravitational contraction and later thermal convection extended th at influence and helped nurture the American resistance to continental drift until the new tectonics appeared in the 1960s.