Echo soundings made over the North Atlantic Ocean and the Mediterranean Sea, using sound pulses from 0.2 to 1 millisecond long, exhibit evidence that several horizontal layers of sediment extend continuously across the nearly flat floors of enclosed basins. In one basin of the Tyrrhenian Sea, the layers which were sampled by coring proved to be alternate layers of sorted coarse clastic materials and clay; basins investigated by others off the coast of California are similar in this respect. The coarse clastic materials are either volcanic ash, probably transported by air, or sorted sand and silt, probably laid down during the terminal phase of turbidity currents. The author suggests that all enclosed basins of the deep sea will be found to contain such layering and that, in general, other abyssal plains will not. These basinal deposits are referred to as sediment ponds because of their mode of occurrence. Sequences of bedding have been found by echo sounding which have the appearance of having been formed in an enclosed basin and later distorted by tectonic action. The suggestion is made that the flysch of the Alps and other similar sedimentary rocks may have formed originally in ancient enclosed basins.

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