National Geographic : 1966 Nov
Mojave, among others. Some of the regional structures in these remote areas would require many years to decipher by ground methods-for example, the eroded fractures and huge lava flows in Niger's Air Mountains (pages 658-9), which lie in the part of the Sahara traversed by Victor Englebert in his salt caravan article in NATIONAL GEO GRAPHIC for November, 1965. Pictures such as that of central Algeria and of Walvis Bay on the coast of South-West Africa (pages 658-9) tell much about how sand dunes form, evolve, and move things which we understand very imperfectly so far. Sel dom does one see a more striking natural pattern than that of the enormous seif dunes near Walvis Bay-200-foot waves of sand that parallel the prevailing winds for as much as a hundred miles, in lines so straight as to suggest man-made structures. One scientist has suggested that these dunes may be analogous to the Martian "canals." Space photographs may throw new light on the theory of continental drift, which holds that the continents have moved slowly to their present positions, like drifting ice floes. The western coastline of Africa and the eastern coastline of South America, as a case in point, could fit together like pieces of a jigsaw puzzle, suggesting that these continents were once one but have since separated. If this is true, there should be considerable similarity in the structural patterns of the ancient Precambrian rocks of the coastal regions of the two continents. Pictures like that of Walvis Bay, which show far more geologic detail than maps even though the scale is actually smaller, may help prove or disprove this theory. An Aggressive Stream Can "Pirate" Water The geographer finds much of interest in the extraordi narily barren and remote region of the Arabian Peninsula (page 660). The fantastically intricate pattern of the great Wadi Hacjramawt shows how much control geologic structure has over drainage. Sharp-eyed readers will de tect, in the top center of the picture, several valleys crossed by another valley. This is an example of incipient "stream piracy," in which one stream, cutting a path more rapidly than others, slashes across them and diverts their waters. A photograph such as that of west Texas (page 666) holds substantial interest because-unlike the uninhab ited areas shown in this series-it reveals much evidence of man. The checkerboard pattern obviously indicates farmland, while the apparently undivided land at upper left, too dry for farming, serves chiefly for cattle raising. The great Permian Basin oil field shows as a faint array of dots (extreme right center). Many other man-made features are visible-roads, the Midland-Odessa airport, and even a dark blob of smoke from a carbon-black plant near Odessa. The oceans have traditionally been studied on or in the water. But the oceanographer now foresees many applica tions of pictures made from satellites. They reveal such things as distribution of river sediment in gulfs, as in the photographs of the Colorado River (pages 649-50) and Yangtze River mouths (page 662); the topography of the 652 (ABOVE) BY DEAN CONGER (C N.G.S. SOUTHEAST FLORIDA Cotton-boll clouds shadow the toe of Florida and camouflage its largest lake-Okeechobee, center. Thunderheads, building up over the Everglades, loosed torrents of wind-lashed rain later in the day. Surf outlines the boundary between land and ocean. From Cape Kennedy's arrowhead tip, upper center, astronauts speed into space; Gemini 5, from which this picture was made, lifted off 27 hours and 18 orbits earlier. Dangling like an elongated earring, the island playground of Miami Beach sells the glitter of a sun-sprayed sea (above). Off Key Largo, to the south, the underwater beauty of John Pennekamp Coral Reef State Park can be sensed even from 140 miles aloft.