vi ULU-I-NDALI 89 



description of their characters is given on page 335. Such tuffs 

 extend as high as 300 feet above the sea on the north-west slopes, 

 where there are exposures, 10 to 12 feet in thickness, in the dry- 

 stream courses ; and here they may be seen overlying the basalt 

 and rudely bedded, dipping away from the summit at an angle 

 of 15 degrees. 



The grey olivine-basalts of Ulu-i-ndali, which often look like 

 clinkstone, range generally in specific gravity from 2*9 to 2-95. 

 They contain microporphyritic olivine in abundance, which is 

 usually more or less haematised and in extreme cases of the change 

 looks like brown mica. Most of them are referred to genus 16 of 

 the olivine class and their characters will be found described on 

 page 258. The felspar-lathes are stout and show sometimes 

 lamellar twinning, and on account of their large size ('2 to "5 mm 

 in average length) the rock acquires a doleritic texture. They 

 display as a rule a flow arrangement around the olivine crystals. 

 Augite granules occur in great abundance, and there is rarely any 

 interstitial glass. 



These grey olivine-basalts are as a rule non-vesicular, but rocks 

 with minute irregular cavities, though without glass, occur scantily 

 on the upper slopes. They come near to the grey olivine-basalts 

 of the hill of Koro-i-rea in the Solevu district, as described on 

 page 77 ; but they differ in their doleritic or coarser texture, the 

 felspar-lathes in the last-named locality being much smaller, their 

 average length being *I2 mm. 



The blackish basalts, mostly characteristic of the lower slopes 

 of Ulu-i-ndali, vary somewhat in character ; but they may on the 

 whole be regarded as surface forms of the more deeply situated 

 grey basalts which are practically holocrystalline. The rock of 

 this kind that prevails on the south and west sides has a specific 

 gravity of 2 - 96. It is referred to the same genus (16) as the grey 

 basalts, but differs from them in the circumstance that the 

 microporphyritic olivine is serpentinised and not haematised, and 

 in the occurrence of a fair amount of devitrified interstitial glass, to 

 which probably the dark colour of the rock is due. . . . The dark 

 aphanitic basalt, with flinty fracture and a specific gravity of 3'00, 

 that is displayed in Vatu Vono Point, is merely a compact surface 

 variety of the more coarse-textured grey basalts, being referred to 

 the same genus. Here there is a great abundance of micro- 

 porphyritic olivine in a groundmass of parallel felspar-lathes and 

 augite grains ; but the felspars are unusually small, averaging 

 •1 mm. in length ; and there is a much larger amount of fine 



