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Diversity Shape Mode: The marine bivalves show remarkable diversity shape mode in shape and mode of life. Most, however, are sand dwellers and live just below the surface of the muddy sand where they keep in contact with food-laden ocean water by means of two fleshy, tubular siphons. In the Venus clams, the surf clams (Alactridae), and Lucine clams the siphons are very short, while in others, such as the common soft shelled clam {My a) and the angel wing of Florida (Barnea costata) which live far below the surface, the siphons are encased in a very long muscular tube.
It consists mainly of hydrated oxides of ferric iron and aluminum, with little quartz. Contrary to the usual mode of weathering, silica also is removed in the formation of laterite. Bauxite is a rare type of laterite from which most of the iron has also been removed.Detrital Deposits.—These constitute the great bulk of sedimentary rocks. Sorting of detrital deposits is highly variable and depends on theirdistance from their source and their mode of transport. Studies of mineral composition, bedding, grain size, heavy accessory minerals, the shape and rounding of grains, and the manner of cohesion may yield clues to the mode and direction of transport and to the nature and location of the source rocks.
The successful development of a dual-mode vehicle would be of great importance to many urban areas. Most cities in the U.S. have rail lines that penetrate or closely approach downtown cores. The dual-mode vehicle overcomes a major limitation of these rail rights-of-way. The limited areas that the rails serve are inadequate for a complete urban transportation system. A dual-mode vehicle would operate on the streets and on rails. |
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