326 A NATURALIST IN THE PACIFIC CHAP. 



cracks in the rock-mass are rilled with a quartz mosaic. The tests 

 of the foraminifera remain calcitic ; but their cavities are filled 

 either with the matrix or with calcite or with a colourless fibro- 

 radiate mineral polarising in blackish-blue hues. 



D. From the south shore of Savarekareka Bay. . . . The 

 locality is described on page 190. 



This is a bright green hard compact rock with flinty fracture 

 and not effervescing with an acid. In the slide it shows a few 

 casts of foraminifera of the " Globigerina " type in a matrix com- 

 posed mainly of fine debris ('Oi-'O4 mm.) of felspar and pyroxene 

 with much greenish opaque amorphous alteration products. The 

 abundance of pyroxene is remarkable. The material of the tests 

 of the foraminifera is altogether replaced by a greenish yellow 

 mineral, occurring in grains and radiating prisms, apparently 

 epidote. 



E. From an elevation of 950 feet on Mount Thambeyu. . . . 

 The locality is described on page 177. 



A hard dark grey rock containing 10 or 15 per cent, of 

 carbonate of lime and showing fine specks of pyrites. In the 

 slide are displayed numerous tests of foraminifera of varying size 

 up to *5 mm. ; scattered patches of pyrites ; fragments of a semi- 

 vitreous basic rock, not exceeding '15 mm. in diameter, and of 

 plagioclase and pyroxene ; in a matrix of the finest debris of the 

 same materials impregnated with granules of calcite. The tests of 

 the foraminifera are filled either with calcite, showing a black cross 

 in polarised light, or with a zeolite, or with pyrites, or with the 

 matrix. 



SUBMARINE BASIC TUFFS OF MIXED COMPOSITION 



These tuffs, which are composed not only of palagonitic 

 materials but also of the fine detritus of usually semi-vitreous 

 basic rocks, rank first in frequency amongst the volcanic sedimen- 

 tary deposits of the island. In their character they pass on the 

 one hand into the foraminiferous volcanic mud-rocks or clay rocks 

 and on the other into the tuff-breccias and tuff-agglomerates. We 

 have here a series beginning with the agglomerate and ending 

 with the clay that represents in a general sense the successive 

 stages of the degradation of the same materials. 



These tuffs occur at all elevations from the sea-border, where 

 they may form the shore-cliffs, to the upper slopes and summits of 

 the mountain-ranges, where they are found at elevations between 



