. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] ESTUARIES, DELTAS, SHELF, SLOPE 645 deposits may be completely different at equal depths and 50 yd apart as a result of local shelters. Conversely, rocky grounds exist in shelf areas where current velocities do not seem to be especially high, for example on outer shelves off Southern California (Revelle and Shepard, in Trask, 1939), and in East Antarctica, where they often correspond to j^laces from which the inland ice has retreated only recently (Lissitzin and Jivago, 1958). An interesting type of deposit on she
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 3] ESTUARIES, DELTAS, SHELF, SLOPE 645 deposits may be completely different at equal depths and 50 yd apart as a result of local shelters. Conversely, rocky grounds exist in shelf areas where current velocities do not seem to be especially high, for example on outer shelves off Southern California (Revelle and Shepard, in Trask, 1939), and in East Antarctica, where they often correspond to j^laces from which the inland ice has retreated only recently (Lissitzin and Jivago, 1958). An interesting type of deposit on shelves consists of the sediments situated in front of present or former glaciated areas in America, North Europe and Antarctica. Those lying off More and Romsdal, Norway, have been studied by Holtedahl (1955) and Berthois (1957) (Figs. 20 and 21). The samples include stones, sand, silt and clay in variable percentages. "The medians show wide 23 mm 1480^ 360m M. 3 mm 50 M Fig. 21. Cumulative curves of particle diameters of glacial marine sediments of continental shelf and slope off More and Romsdal, West Norway. Figures on curves indicate the depths of samples in fathoms. (From Berthois, 1957.) variations at the same depths, both sand and gravel being found in the de- pressions as well as on the shallow ; Only pebbles are dredged in some places. Their roundness is not at all typical of a former coastal environment: on the contrary, they closely resemble glacial pebbles, and the bulk of the sedi- ments has the character of glacial tills. Some samples consisting of sand and lying at 100 fm are fairly well sorted and might represent an old shoreline, but generally the sorting is extremely poor and the size distribution curves show such individual characteristics that it is difficult to classify them. The nature of the pebbles covers a wide range of crystalline and metamorphic rocks; limestones, sandstones and flints are sometimes present. These data point to
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