22 THE OCEAN FLOOR 



summits which are at present lying in the Pacific Ocean 

 at depths of between 2,500 and 6,000 feet. The carbon 

 dioxide simultaneously released, amounting to about 

 5% in weight of the water, has given rise to the thick 

 layers of calcareous sediments covering parts of the 

 ocean bed.* 



It seems reasonable to assume that the effusion of 

 magma over the ocean floor, as well as the release of 



k SLOPING 



Fig. 9. Vertical section of a guyot 



magmatic volatiles, has varied greatly in intensity during 

 the earth's history. If the origin of the Mid-Atlantic 

 Ridge is placed in the early and late Tertiary, as Ivan 

 Tolstoy and others assume, a great release of crustal 

 water and other volatiles must in fact have taken place 

 in the course of the last 100 million years, and only a 



* Another possible source of water which seems to have 

 been overlooked by American authors is that contained in the 

 clay minerals.^ 



