xii THE THAMBEYU RANGE 177 



for night-shelter by those exploring the range. The lowest, 1,500 

 feet above the sea, is the Taloko Cave (na-ngara-taloko). The 

 highest is the Ndromo Cave, 1 2,100 feet, known to the natives as 

 " na-ngara-vatu-ni-ndromo." Like most of the caves all over the 

 island they occur at the junction of the agglomerates and tuffs, 

 and are to be attributed to the more rapid weathering of the 

 underlying tuffs. ... In describing the results of my examination 

 of this mountain-ridge, I will deal in succession with the tuffs, the 



Ideal Section of Thmbeyu.. 

 2600 ft. ^^^ m}7e ^ ht 



Pyroxene -andesites 

 Foraminiferoiis Tuffs and Clays 

 Volcanic agglomerates. 



agglomerates, the junction between these two deposits, and the 

 axis or core of basic rocks. 



(1) The submarine tuffs and tuff -clays. — As exposed in the 

 stream-courses near and at the foot of the mountain and as high 

 as the Taloko Cave, these deposits are bedded horizontally. At 

 higher levels, owing to insufficient exposure the bedding is not so 

 clear. Up to 700 or 800 feet coarse palagonite-tuffs prevail ; but 

 they do not effervesce with an acid, and apparently contain but 

 scanty organic remains. At 950 feet coarse and fine sedimentary 

 tuffs alternate, the last being greenish foraminiferous tuff-clay 

 rocks, somewhat compacted and containing 10 per cent, of car- 

 bonate of lime. The tests of the foraminifera, which are abundant 

 and of the Globigerina type, are filled with calcite. Several frag- 

 ments, of a semi-vitreous basic rock, not however exceeding "2 mm. 

 in size, are inclosed in the deposit ; but the mass of it is made up 

 of yet finer materials of the same rock, palagonitic detritus, plagio- 

 clase fragments, fine calcitic debris, tests of foraminifera, &c. 

 These fine tuff-clays were evidently formed in relatively deep- 

 water. 



At the Taloko Cave (1,500 feet), where there are exposed rather 

 coarse tuffs containing bands about a centimetre thick of a fine 

 clay-tuff, the last-named effervesce freely with an acid, whilst 



1 A kind of "edible" bird's-nest is found in this cave. 



N 



