XIII NA SUVA-SUVA 



193 



Through the kindness of Mr. F. Spence, I was able to make 

 use of a track cleared to the top of Na Suva-suva. This eminence, 

 which forms a conspicuous landmark for many miles, both land- 

 ward and seaward, has a rounded summit and is to all appearance 

 an old volcanic neck. It is composed in mass in its upper half of 

 a heavy dark olivine-basalt (sp. gr. 3-01), seemingly non-columnar, 

 and referred to the highly basic rocks forming genus 16 of the 

 olivine-basalts. There is such a thick soil-cap on the lower slopes 

 that I was unable to ascertain the character of the rocks there. 

 It is, however, noteworthy that a very similar olivine-basalt (sp. gr. 

 2-99) crops out on the coast south of this hill and to the east of 

 Naindi Eay. They both contain abundant small olivine-pheno- 

 crysts and a little residual glass, the felspar-lathes averaging 

 ■I — •14 mm. in length. Since their localities are rather more than 

 a mile apart, it is not possible to say without a further examination 

 of the locality whether or not we have here the same intrusion. 



On the coast between Naindi Bay and Salt Lake Passage, 

 calcareous tuffs, probably fossiliferous, are occasionally exposed in 

 the low spurs descending to the sea, whilst islets of elevated reef- 

 rock front the beach. 



The coast immediately west of the Salt Lake Passage is of 

 exceptional interest. Here the sea-cliffs and the shore-flat are 

 formed of an agglomerate tuff penetrated in all directions by veins 

 of calcite, an inch and under in thickness. The matrix of this 

 deposit, which is a little calcareous, is principally made up of frag- 

 ments, ranging up to 3 or 4 millimetres in size, of vacuolar pala- 

 gonite, the minute vesicles being filled with some alteration pro- 

 duct. It also contains large macled augite crystals 5 or 6 mm. in 

 size, which can be picked out in numbers by the fingers. The 

 blocks vary from a few inches to two feet across, and are usually 

 composed of an augite-andesite, containing large porphyritic 

 crystals of augite, and are often amygdaloidal, the amygdules, 3 or 

 4 mm. in size, being formed of a zeolite. But blocks of very 

 different rocks also occur in this agglomerate tuff. One, about 

 two feet across, was composed of a coarsely crystalline diorite 

 made up, as described on page 251, of large crystals of hornblende, 

 2 to 2-5 centimetres long, and of large opaque crystals of acid 

 labradorite. Another was made of hornblende-hypersthene ande- 

 site belonging to the ortho-phyric order of that sub-class (see 

 page 299). There is a little altered glass in the groundmass, and 

 large secretions of brown hornblende, more than an inch in size, 

 are to be observed in the rock. 



O 



