Historical geologists

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Historical geologists, in the olden days, pieced together that narrative. Economic geologists, in their pragmatic way, cared less. In describing the minable Martinsburg-the blue-gray true unfading slate-C. H. Behre, Jr., wrote in i933, “Sedimentary rocks are often compressed from the sides through what may be loosely described as shrinking of the crust of the earth; how this shrinking is brought about is, for the present purpose, beside the point. It has the wellrecognized effect, however, that layers or bedding planes are wrinkled or thrown into ‘folds.’ ” By the nineteen-seventies, what Behre had loosely described was widely believed to be the impact of one continent colliding with another, as Iapetus, tl1e proto-Atlantic ocean, was closed and the suture of the two continents became the spine of the Appalachians. The conference room amsterdam successive pulses of orogeny-Taconic, Acadian, Alleghenianwere attributed to the irregular shapes of shelves and coastlines of the continents. Where they bulged, the action would have an early date, and especially where some cape, point, or peninsula had a similar feature coming from the opposite side. Such headlands, in advance contact, were said to have produced the Taconic Orogeny. Great bays, eventually coming against one another, set off the Acadian Orogeny. The Alleghenian Orogeny was the final crunching scrum, completing the collision. The apparent suture was a line running through Brevard, North Carolina, more or less connecting Atlanta, Asheville, and Roanoke, not to mention Africa and America. The Martinsburg seafloor and the underlying carbonate rocks had unquestionably been broken into thrust sheets and shuffled like conference room eindhoven cards. Uplifted with their Precambrian basement, they had, in perfect harmony with the Old Geology, become mountains that shed their sediments-shed their elastic wedges-and buried the Martinsburg deep enough to turn it into slate, buried the carbonates deep enough to turn them into marble. Thus, plate tectonics fit. Plate tectonics may have restyled the orogeny and dilapidated the geosyncline, but it fit the classical evidence.

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