VIII NA RARO 125 



2j miles distant from Na Raro, and though situated in the 

 heart of the island it is only about 100 feet above the sea. The 

 track first passes through a district of foraminiferous tuffs and clays 

 reaching up to 200 or 250 feet. Afterwards a broken country 

 extending up to 800 feet is traversed. Here prevail agglomerates 

 and tuff-agglomerates derived from aphanitic augite-andesites.^ 

 One then descends into a valley about 600 feet above the sea, 

 and from this place the ascent of the mountain proper begins. 



The ascent at first is fairly steep, dacitic tuffs prevailing up to 

 1,000 or 1,100 feet above the sea and forming in places precipitous 

 cliff-faces. Large masses of hornblende-andesite lie on the slopes. 

 The dacitic tuffs distinguish Na Raro from all the other peaks of 

 hornblende-hypersthene-andesite rocks that I examined. They 

 seem generally to have been stripped off by the denuding 

 agencies ; and only at times, as around the slopes of Ndrandramea 

 and Thokasinga, are to be found the remains of agglomerates of 

 the same formation. In the case of Na Raro, however, the tuffs 

 differ somewhat in their components from the rocks forming the 

 mountain mass. The tuffs are derived from a hornblende- 

 andesite of dacitic type ; whilst the massive rocks of the mountain 

 are of hornblende-hypersthene-andesites, without porphyritic 

 quartz, but approaching the dacitic habit. 



The tuffs of Na Raro, which are sometimes compacted and at 

 other times rather friable, do not display bedding. They contain 

 a little lime ; but I found no tests of foraminifera. They are 

 composed of fragments, up to a centimetre in size, of a dacite 

 displaying brown hornblende, plagioclase, and quartz in a 

 microfelsitic groundmass, together with a few fragments of a 

 semi-vitreous basic andesite. 



Above 1,100 feet the tuffs give place to the massive hornblende- 

 hypersthene-andesite. At an elevation of 1,450 feet, a shoulder of 

 the mountain is reached, near the top of which is the cave above 

 mentioned. Crossing the shoulder one descends for 100 or 150 

 feet into a gap, thus reaching the foot of the precipitous northern 

 peak, which rises up like a wall for a height of from 900 to 1000 

 feet overhead. It is in mass of the andesite just mentioned, many 

 of its faces presenting inaccessible cliffs displaying seemingly no 

 structure. This peak is somewhat lower than the southern peak. 

 I placed its height at 2,270 feet, which, taking the total elevation 

 of the mountain at 2,420 feet, as given in the chart, makes the 

 difference 150 feet. A deep and broad cleft, that goes half-way 

 1 Referred to genera 16 and 20 of the augite-andesites. 



