. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 2] ABYSSAL PLAINS 335 contain beds of graded calcareous sand containing fragments of the calcareous alga Halimeda and shallow benthonic Foraminifera (Ericson, Ewing and Heezen, 1952). The depth of the deeper trench abyssal plain ranges only a few fathoms from 4585 fm. The Puerto Rico Trench plain seems to be the widest and most extensively developed of all trench plains. Although most trenches are not well enough surveyed to reveal the maximum width of other trench plains, it is known that the Tonga Trench and the Ku
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. SECT. 2] ABYSSAL PLAINS 335 contain beds of graded calcareous sand containing fragments of the calcareous alga Halimeda and shallow benthonic Foraminifera (Ericson, Ewing and Heezen, 1952). The depth of the deeper trench abyssal plain ranges only a few fathoms from 4585 fm. The Puerto Rico Trench plain seems to be the widest and most extensively developed of all trench plains. Although most trenches are not well enough surveyed to reveal the maximum width of other trench plains, it is known that the Tonga Trench and the Kurile-Kamchatka Trench have relatively narrow trench plains, reaching maximum widths of 2 or 3 Fig. 18. Puerto Rico Trench Abyssal Plains. (After Ewing and Heezen, 1955.) Although trench plains are common along the axis of the Peru-Chile Trench, these plains do not appear to be continuous over any considerable distance along the trench axis. Enclosed basins in the continental margin which lie downhill from adjacent land-masses generally contain abyssal plains. Small abyssal plains are found in the floor of the Cariaco Trench, a 750-fm-deep depression in the continental shelf north of Venezuela (Heezen et al., 1958). The flat floors of many fjords are probably similar in origin to the trench plains mentioned above. Indeed, much of the floor of the Lake of Geneva in Switzerland is of abyssal-plain character. This plain lies at the foot of a large cone spreading out from the mouth of the Rhone. These features, although similar in form and almost. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hill, M. N. (Maurice Neville), 1919-. New York : Interscience Pub.
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