108 THE OCEAN FLOOR 



deposits on land. It appears that a general evolutionary 

 trend can be demonstrated as having occurred simul- 

 taneously in all parts of the world within, say, the 

 latitudes of 40° N. and 40° S. 



Recent work by Brotzen and Dinesen on forams 

 from cores taken in the central Pacific Ocean has 

 proved that an abrupt change in the fauna occurred in 

 a core at a depth of 4^2 meters below the sediment 

 surface. Work by Kolbe has shown the occurrence 

 of an equally abrupt change of the diatom flora in 

 another long core from the same region.^ Research 

 directed toward finding similar unconformities in cores 

 from the other two oceans is now proceeding. A re- 

 markable find by Kolbe in two cores from the equatorial 

 Atlantic is the occurrence of typical fresh-water dia- 

 toms in considerable numbers. Since this find was made 

 in localities several hundred miles from the coast of 

 northwest Africa, the origin of these fresh-water dia- 

 toms is puzzling. 



Research of considerable interest pursued for some 

 years in Goteborg by Rotschi and Berrit has been 

 devoted to the ferrides present in cores, from both the 

 central Pacific and the equatorial Atlantic, notably the 

 elements Fe, Mn, Ni, and to a certain extent Ti.^^ The 

 origin of iron and manganese in deep-sea sediments 

 is not completely cleared up. Arrhenius and others are 

 inclined to distinguish between "halmyrogenic" man- 

 ganese and manganese of minerolytic origin, the latter 

 largely derived from submarine volcanic debris which 



