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.i 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., 

 arid 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 1 1 feet above its present level. 



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

 came upon an exposure of neariy 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, 

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

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

 oraminifera of the globigerina type, their cavities being generally 

 illed with palagonitic material. 



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

 j.bout 250 feet above the sea, the impure foraminiferal limestones 

 k gam 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 

 1 idicated mosaic the commencement of recrystallization. In the 

 c ise of those of the upper locality the calcitic material of the 

 g roundmass has more completely recrystallized, and shows a fairiy 

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

 ii crusted above by a layer, 3 inches thick, of a white crystalline 

 h nestone, looking like statuary marble, and inclosing portions of 

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

 a: amed in the slide, exhibits itself as formed in mass of crystalline 

 CJ Icite, displaying a regular mosaic, and inclosing small fragments 

 * These foraminiferal limestones are described on p. 319. 



K 2 



