SECT. 2] 



CONTINENTAL, SHELF AND SLOPE 



303 



Bank near Lith, to the south of Jidda, has been described by Guilcher and 

 Nesteroff (1955), who had an opportunity of examining this submarine area 

 during the Calypso Expedition in 1951-1952 (Fig. 12). The lofty mountains of 

 Asir are bordered to the south-west by a series of large fault scarps ending on 

 the coastal plain of El Tihama. The suljmarine to])ography includes two steps 

 perfectly distinct from one another : the higher one, near land, occurs at 30- 

 45 fm, the lower one lies at 350-400 fm. The scarp between the two, which was 

 sounded near Abulat Island, is })recipitous and runs in the same direction as the 

 general trend of the Red Sea graben. Abulat Island, on the higher platform, 



Scale in 

 foreground 

 Or 



500 fm 



•1 Noutica 

 mile 



Fig. 12. Block diagram of the faulted shelf at Abulat Island, Saudi Arabia, Red Sea 

 (40°E, 20°N). Many coral knolls on upper platform. ¥, faidt. Crosses, basement. 

 Dots, coral and coral mud (the thickness is hypothetical). Maximum height of Abulat 

 Island above sea-level: 100 ft. (Modified from Guilcher, 1955.) 



consists of uplifted corals of late Pleistocene or Recent age dissected by many 

 small fault scarps ; the main direction of these scarps is again NW-SE. From 

 the lower platform long, narrow ridges rise abruptly to the sea-surface ; these 

 consist of coral reefs in their upper parts and are supposed to have initially been 

 small faulted blocks rising moderately from the general level of the platform 

 on which corals have grown during a comparatively slow subsidence. These 

 high ridges are referred to as shaban (singular, shah) by the Arabs. Farther to 

 the north, some submarine and coastal features off the Arabian coast, at the 

 entrance to the Gulf of Aqaba, have been briefly described by Schick (1958). 

 The Midian Islands, which are composed of a dozen islands and islets and in- 

 numerable reefs, stretch in a long line parallel to the coast, from which they are 



