158 A NATURALIST IN THE PACIFIC chap. 



gorge of the Natoarau river on the east, the bottom of which is 

 750 feet above the sea, and from here the climb begins. One 

 ascends the bed of the stream course, clambering over slippery 

 rock surfaces up to 1,2c D or 1,300 feet, where the stream is left, 

 and the mountain-slopes, often steep and precipitous, are then 

 followed to the summit, 2,000 feet in height. Coarse and fine 

 palagonite-tuffs and agglomerate-tuffs of the same character are 

 exposed on the surface from the commencement of the ascent up 

 to 1,850 feet ; but they are displayed much more extensively in the 

 stream-course than in the soil-covered upper slopes. 



The tuffs are grey except when hydrated, when they turn yel- 

 lowish-brown. Some of them contain lime, as much at times as 

 10 or 12 percent; whilst others possess little or none. Tests of 

 foraminifera are not infrequently inclosed, even as high as 1,850 feet. 

 A description of one of these tuffs containing a few tests of Globi- 

 gerina, which was obtained at 1,200 feet, is given on page 331, under 

 sample D. It will be there seen that they are derived from different 

 basic rocks, some containing but little glass, others mainly vitreous, 

 only the more glassy constituents being palagonitised. The palago- 

 nite-tuff sandstones exposed in large blocks on a bare spur at 1,850 

 feet contain 12 per cent, of lime, the largest tests of foraminifera being 

 not over half a millimetre.-^ These tuffs occasionally show bedding. 

 At 1,000 feet they dip gently to the S.S.W., and at 750 feet 

 they are inclined about 15° in the same direction. In this last 

 locality they consist of alternating layers, i to 4 inches in thickness, 



of fine and coarse tuffs, the coarser looking like sandstone 



The blocks in the agglomerate-tuff are sub-angular, and of an 

 olivine-basalt with hemi-crystalline groundmass,^ their size ranging 

 from 2 feet to an inch. I noticed one large block of this rock, 

 measuring 2x1^ X i feet, imbedded alone in the tuffs at 1,200 feet. 

 At one place a tuff containing small fragments of basalt displayed 

 a concretionary structure, indicating probably the proximity of a 

 dyke, the globular masses being 4 feet across. A little lime occurs 

 in the matrix of the agglomerate-tuff 



The summit of the range, 2,000 feet in height, is " ridgy," about 

 half a mile in width, and cannot therefore be described as table- 

 topped. The rocks exposed in blocks on the surface are composed 

 of a semi-ophitic olivine-basalt containing a large amount of inter- 

 stitial glass which shows the fibrous crystallites of the early stage 

 devitrification. It is referred to genus 33 of the olivine-basalts. 



^ They are described under sample E on p. 332. 

 ^ Referred to genus 37 of the olivine-basalts. 



