THE DISTRICT BETWEEN NAINDI BAY AND THE SALT LAKE
Three or four of the peaks of this hilly district rise to about 1,000 feet or rather over, the highest being that of Na Suva-suva, which attains a height of 1,110 feet. Since my acquaintance with this region is incomplete, I will confine my remarks to the localities actually examined.
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 landward 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 Bay. They both contain abundant small olivine-phenocrysts and a little residual glass, the felspar-lathes averaging ·1-·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 fragments, ranging up to 3 or 4 millimetres in size, of vacuolar palagonite, the minute vesicles being filled with some alteration product. 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 andesite 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.