264 



HEEZEN AND MENARD 



[chap. 12 



Compared with faults on land, these "minor" lineations are rather large 

 features. But despite their size, only a few areas of the oceans have been 

 sufficiently well sounded that such features can be delineated. It is only possible 

 to map minor lineations when precision sounding equipment is employed on 

 ships positioned by precision electronic navigation systems. A few such areas 

 (Fig. 23) have been surveyed in the Pacific (Menard, 1959). 



i. Aseismic ridges 



A significant discovery of the Meteor Expedition was that a continuous ridge 

 runs in a southwesterly direction from the vicinity of Walvis Bay, Southwest 



1000 METERS 



2090 



3000 



MARVIN RIDGE 



LOMONOSOV RIDGE ■''"* 



8e"45 N 



Eost-West Profile ol 28°30'S 



l-JOE 



3000 



4000 



5000 



J 



100 NAUTICAL MILES 



Fig. 27. Profiles of the Lomonosov Ridge in the Arctic Ocean and the Walvis Ridge in 

 the South Atlantic. These two ridges are excellent examples of the asymmetrical, 

 aseismic ridges. (After Heezen and Ewing, 1960.) 



Africa (Fig. 27). The discovery of this feature strongly influenced the German 

 investigators (Stocks and Wiist, 1935) and a now-familiar herringbone pattern 

 of ridges in the whole Atlantic was postulated. Not many of these postulated 

 ridges survived later investigation. The Walvis Ridge strikes out from the 

 continent seaward of the Angola u])lift. The ridge is strongly asymmetrical, 

 narrow and steep-sided on the south. The main ridge typically has two crests 



