VA-LILI 



145 



In a cliff-face of the adjacent main range there are displayed 

 an agglomerate of basaltic andesite and a pitchstone-breccia, com- 

 posed of fragments of but little altered basic glass, the interstices 

 being filled up with palagonite. In the case of the Kiombo flow 

 I have endeavoured to explain the origin of a closely similar pitch- 

 stone-breccia (page 92). 



(5) The Sea-border and the Low-lying Districts at 

 THE Base of the Va-lili Range.— It may be generally re- 

 marked that palagonite-tuffs and clays, often foraminiferous, prevail 

 in these localities. Thus in the sea-border between Waiwai and 

 the mouth of the Ndreke-ni-wai basic agglomerates are displayed 

 where the mountains approach the coast ; but further west a broad 

 tract of undulating land, elevated usually 100 to 300 feet, inter- 

 venes between the range and the sea-border, and here coarse and fine 

 palagonite-tuffs predominate On the north-west the forami- 

 niferous tuffs and clays of the Ndreketi plains approach the Va-lili 

 range in the vicinity of Vuinasanga, and extend for at least 200 or 



300 feet up its sides At the east end of the range, where the 



slopes descend to the plains of the Waisali valley, a little west of 

 Mbale-mbale, there are exposed bedded palagonite-tuffs, tilted up 

 at an angle of about 20° to the south-west. They contain a little 

 lime and display microscopic tests of foraminifera, the palagonite 

 being minutely vacuolar, the cavities also being iilled with the 

 altered glass. I noticed those submarine deposits at an elevation 

 of 100 feet, but probably they reach much higher. 



The inference to be drawn from the data above given concerning 

 the Va-lili range seems clearly to be this. We have here indicated 

 the emergence of a submarine mountain-ridge covered over with 

 palagonite-tuffs and agglomerates, the last being uppermost. These 

 coverings have been in places stripped off by the denuding agencies 

 and the underlying massive basic rocks exposed. These rocks, 

 however, vary much in texture, some being vitreous, as in the case 

 of the pitchstones, others hemi-crystalline as in the case of the 

 basaltic andesites ; and it is to be gathered from this and other 

 similar indications that different submarine vents were formed 

 along a fissure or fissures at the sea-bottom. No evidence of sub- 

 aerial eruptions came under my notice. After the vents became 

 extinct they were buried beneath the palagonite-tuffs and agglo- 

 merates. During and after the emergence the denuding agencies 

 reshaped the surface of the range and left but little of its original 

 form. 



Since it is my object to build up a theory of the origin of the 



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