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Abstract

When the fishermen trawl for bottom fish, scallops, and shrimp, they generally recover loose boulders and break fresh rocks from outcrops. In early geologic studies of the ocean floor off North America, Verrill (1878), Crosby (1879), Upham (1894), Dall and Harris (1892), and Dall (1925) reported the presence of sea-floor outcrops of Upper Cretaceous, Miocene, and Pliocene strata; they dated the outcrops on the basis of many rocks of similar lithology collected by fishermen from Georges Bank and the banks off Nova Scotia. Dredgings by the U.S. Fish Commission recovered a 200-kg boulder in the Gulf of Main and cobbles and pebbles of many kinds of igneous and metamorphic rocks from depths as great as 1,300 m on the continental slope. Verrill (1874, 1883) rightly considered that these materials had been rafted by ice before being dropped to their positions on the ocean floor.

Among the samples from the continental shelf obtained by the U.S. Coast and Geodetic Survey during its nineteenth-century explorations were many that consisted largely of glauconitic sand, with grains composed of internal casts of foraminifers that Pourtales (1850) and Bailey (1856) recognized as similar to those within Eocene strata on shore. Rocks dredged from the banks on the inner shelf between Cape Hatteras and Miami consist of Tertiary limestones that resemble those in outcrops on shore (Pourtales, 1872). They also recovered samples from the top of Georges Bank that Shepard, Trefethen, and Cohee (1934) identified as glacial till and probably salt-marsh peat.

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