66 A NATURALIST IN THE PACIFIC chap. 



of 700 feet and then descends into the Mbua plains. These three 

 almost parallel valleys of the Lekutu and its two tributaries are 

 worthy of a detailed examination. 



The rocks on the surface between Kavula and Wailevu vary in 

 character. Nearer Kavula there appears a blackish compact olivine- 

 basalt (spec. grav. 2'88), showing a little microporphyritic plagioclase 

 and belonging to genus 37 of the olivine rocks. Further on is 

 exposed one of the holocrystalline grey olivine-basalts with 

 porphyritic plagioclase-phenocrysts and specific gravity 2'83. It 

 belongs to the type described in genus 38 of the rocks on page 263. 

 Nearer Wailevu there occurs a blackish porphyritic basalt with 

 scanty olivine and specific gravity 2'8r. It contains but little 

 residual glass and is referred to the porphyritic sub-genus of genus 

 25. In some cliffs at the river-side close to Wailevu, there is 

 displayed a semi-vitreous basaltic andesite, showing large porphy- 

 ritic plagioclase crystals, 3 to 8 mm. Its low specific gravity 

 (2'68) is to be attributed to the large amount of glass in the 

 groundmass. There is a loose mesh-work of felspar-lathes, but 

 the augite is not differentiated. Westward of Wailevu com- 

 mence the decomposing basaltic rocks of the Mbua plains. 



{d) Traverse of the Northern Part of the Summit of Seaturafrom 

 Kavula South-West to Narawai. — The track first lay up the 

 picturesque valley of the Lekutu River to Nandroro, 2 J miles distant 

 and 800 feet above the sea. On the way blackish basaltic rocks of 

 the prevailing Seatura type, with or without scanty olivine, were 

 displayed often in a decomposing condition. At one place a 

 •characteristic grey olivine-basalt, showing opaque porphyritic 

 plagioclase (sp. gr. 2"87), and looking like a porphyrite, was exposed. 

 On account of the abundance of the olivine, it is placed in genus 

 2 of the olivine-rocks. After Nandroro the path lay up the steep 

 mountain-side to a height of 1,500 feet : and afterwards across the 

 summit of the northern part of Seatura, which is here about two 

 miles in breadth. This elevated region is well wooded with here 

 and there a patch of " talasinga " land ; but it is by no means level, 

 its elevation varying between 1,400 and 1,800 feet, and it soon 

 became evident that we were crossing the heads of valleys, some- 

 times 200 or 300 feet in depth, that could only have been excavated 

 by the torrential rains. These streamless valleys afford another 

 indication of the denudation to which this ancient mountain has 

 been subjected. 



The rocks prevailing in this elevated northern portion of Seatura, 

 at heights of 1,500 to 1,800 feet above the sea, are : [a) blackish 



