Ridge Study. Present knowledge, based on 

 studies from surface ships, is analogous to 

 geophysical surveys on land made from alti- 

 tudes of 5,000 m. Submersible craft will en- 

 able scientists to make first-hand observations 

 of the active zones, collect samples and pre- 

 cisely emplace instruments. French and U.S. 

 submersibles and the United Kingdom's deep- 

 towed vehicle Gloria will be used in the area 

 southwest of the Azores (Figure 20). 



Preliminary surveys are now being carried 

 out to select the tectonically most active 

 points in the rift valley of the ridge. The 

 techniques include detailed depth soundings, 

 seismic reflection profiles, ocean-bottom seis- 

 micity data, heat flow data and sediment sam- 



ples. In addition to the United Kingdom, 

 France and the United States, Canada, Iceland 

 and Portugal plan to participate. 



Other studies of processes operating along 

 the Mid-Atlantic Ridge are now being planned. 

 They will emphasize the genesis of metals 

 during formation of the crust and their subse- 

 quent conversion into ore deposits of potential 

 economic interest. 



MANGANESE NODULES 



The third major investigation concerns the 

 origin and distribution of concretions com- 

 monly referred to as manganese nodules. 



N^/— IDOE 73 



VVV I'-''-'' 



PI 20 © Courtesy of National Geographic Society 



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