670 



ARRHENTUS 



[chap. 25 



due to substitution in rutile. The origin of the titanium oxide minerals is still 

 uncertain; it appears probable that the rutile is terrigenous but the anatase 

 might develop in situ (cf. Correns, 1937, 1954; Teodorovich, 1958). 



The ferromanganese nodules range in size from a few microns, suspended in 

 the sediment or coating other minerals, to intergrowths forming slabs several 

 meters wide. The nodules have alternating growth zones of high and low 



Via ^ 



Fig. 8. Zonal growth in manganese nodule (16810, South Pacific). Reflected light, ^^^lite = 

 manganese oxide minerals; grey = goethite; black = mounting medium (polyvinyl 

 resin) filling voids. 



goethite content (Figs. 8 and 9). Detailed information on the distribution of 

 macroscopic concretions over the present sediment sm'face has been obtained 

 through deep-sea bottom photography (Fig. 5) such as by Owen, Shipek, 

 Menard and Dietz in Dietz (1955), Menard and Shipek (1958), Heezen et al. 

 (1959), Shipek (1960), and Zenkevitch (1959), and by sampling of the sediment 

 surface (Skornyakova, op. cit.). Large nodules and crusts appear to accrete on 

 topographic highs, or in other areas with a low total rate of deposition, where 

 the growing nuclei are not buried by other sedimentary components. The rate 

 of accretion was in the range of 10^ to 10^^ cm year~i in a nodule investigated 

 by von Buttlar and Houtermans (1950) apjjlying the results of Goldberg and 



