IX TEMBE-NI-NDIO 131 



times earthy when they contain about 25 per cent, of lime, and at 

 other times more compact with about 45 per cent, of lime, the 

 residue being composed of palagonitic materials, tiny fragments of 

 minerals and of a basic rock, &c} Large shells of Ostraea and 

 Cardium are also contained in these limestones, the valves being 

 detached from each other. The oyster shells project from the 

 weathered surface ; and it is probable that the name of Tembe-ni- 

 ndio, which signifies " the shell of the oyster," may be thus ex- 

 plained. Underneath the foraminiferal limestones in this locality 

 occur bedded coarse tufaceous sandstones, slightly inclined E.N.E., 

 and inclosing waterworn gravel and pebbles. These low limestone 

 cliffs, although about six miles inland, are not more than 120 or 

 130 feet above the sea. In their face there is evidence of an old 

 erosion-line of the river 10 or 11 feet above its present level. 



By following up this branch of the river for a little distance I 

 came upon an exposure of nearly horizontal bedded palagonitic 

 tuffs on its floor and sides. Here a coarse tuff, of which the larger 

 fragments composing it range between 3 and 5 mm. in size, passes 

 upward into a chocolate-coloured compact tuff-clay formed of the 

 same materials, the larger averaging 2 or "3 mm. in size. These 

 tuffs are made up chiefly of a palagonitised vacuolar basic glass, 

 the vacuoles being filled with the alteration products. The lower 

 coarse tuffs contain very little lime, probably not over i per cent., 

 and exhibit no organic remains in the slide. The upper fine tuffs 

 have 3 or 4 per cent, of lime, and inclose numerous minute tests of 

 foraminifera of the globigerina type, their cavities being generally 

 filled with palagonitic material. 



Further up the valley about a mile above Tembe-ni-ndio, and 

 about 250 feet above the sea, the impure foraminiferal limestones 

 again appear ; but they here exhibit an important difference in 

 texture. In the groundmass of those of the lower locality, the 

 calcite is granular and loosely arranged, or displays in an obscurely 

 indicated mosaic the commencement of recrystallization. In the 

 case of those of the upper locality the calcitic material of the 

 groundmass has more completely recrystallized, and shows a fairly 

 clear mosaic ; whilst in one place the rock was overlain or rather 

 incrusted above by a layer, 3 inches thick, of a white crystalline 

 limestone, looking like statuary marble, and inclosing portions of 

 a material like that of the rock beneath it. This last, when ex- 

 amined in the slide, exhibits itself as formed in mass of crystalline 

 calcite, displaying a regular mosaic, and inclosing small fragments 



^ These foraminiferal limestones are described on p. 319. 



K 2 



