PLATE XVIII. 
Fig. 1. Section of nucleus of manganese nodule from Station 286; 2376 fathoms, South Pacific. In the 
manganese forming the ground-work of the preparation, there are embedded irregular, triangular, 
elongated, or quadrilateral fragments, having a yellowish tint, and formed of successive zones of 
different shades of colour ; very often there is a hoUow centre, in which crystals of zeolites are 
sometimes formed. In polarised light these fragments are birefrangent, like palagonite, and are 
believed to be altered fragments of basic volcanic glass (magnified 146 diameters). 
Fig. 2. Section of nucleus of manganese nodule from Station 276 ; 2350 fathoms. South Pacific. This nucleus 
is formed by an aggregation of greenish, vesicular, volcanic lapilli, enclosing little lamellss of plagio- 
clase and sections of olivine almost entirely replaced by limonite mixed with manganese, and in 
addition some grains of augite. These are splinters of basaltic rock, with an altered vitreous base, 
the different lapilli being cemented by fibro-radiate bands of zeolites, for min g a mammillated coating 
around each splinter (magnified 145 diameters). 
Fig. 3. Section of nucleus of nodule from Station 276; 2360 fathoms, South Pacific. This nucleus is com- 
posed of volcanic fragments of a vitreous nature, transformed into palagonite. There are numerous 
areolar cavities lined or filled with zeolites, besides numerous lamellae of plagioclase. The two 
lapilli partially represented in the figure are surrounded by zeolitic zones, the interspace being 
filled with earthy matters and peroxide of manganese (magnified 60 diameters). 
Fig. 4. .Section of nucleus of nodule from Station 276 ; 2350 fathoms. South Pacific. This nucleus consists 
of a fragment of palagonite of a red colour, in which there are some lamellae of plagioclase. The 
vesicles are everywhere occupied by fibro-radiate colourless zeolites, in a thick layer towards the 
interior, but in concentric zones towards the external border, the empty space in the centre being 
frequently filled by manganese or muddy matters. The characteristic fractures depending on the 
perlitic structure are in this specimen more circular than is usually the case (magnified 145 dia- 
meters). 
