64 A NATURALIST IN THE PACIFIC chap. 



On the south-eastern slopes of the mountain between Ndawa- 

 thumi (inland) and Korolevu (at the coast), somewhat similar 

 basalts with scanty olivine are exposed (sp. gr. 2*86 — 2-91). Some 

 of them show the felspar-lathes of the groundmass arranged in a 

 plexus (genus 25), whilst others exhibit flow-structure (genus 37), 

 the average length of the lathes varying in different localities be- 

 tween -15 and - 2i mm. All display scanty residual glass. On the 

 shores of Wainunu Bay between the Wainunu and Korolevu 

 rivers occur porphyritic basaltic andesites with a considerable 

 amount of glass in the groundmass. There is exposed on the right 

 side of the mouth of the last-named river a highly basic variety of 

 olivine-basalt with a specific gravity of 3 07. It is referred to 

 genus 15 (described on page 258), which includes the most basic 

 rocks in my collection. There are in this rock no plagioclase 

 phenocrysts and the felspar-lathes of the groundmass are relatively 

 infrequent, whilst olivine and augite occur in abundance. There is 

 little or no residual glass. In the district of Tongalevu blackish 

 olivine-basalts and basaltic andesites of the usual character are 

 found. In the Na Suva range, which lies two miles inland from 

 the shores of Nasawana Bay and forms the southerly extension of 

 the mountain, a somewhat compact variety of olivine-basalt (sp. gr. 

 2*92) prevails up to the summit, 1,550 feet above the sea. It is in- 

 cluded in genus 37 of the olivine-basalts. In the length of the 

 felspar-lathes (-15 mm.) it belongs to the Seatura type of these 

 dark basalts. 



(b) The Western Slopes of Seatura. — Here overlooking the 

 plains north of the Ndama River the same olivine-basalts and 

 porphyritic basaltic andesites occur. The vegetation is of the 

 scanty " talasinga " character, and since there is little or no soil-cap 

 the disintegration of the rocks has been very great, often extending 

 to a depth of 10 or 12 feet. It is remarkable that this disin- 

 tegration is most marked in the " talasinga " and similar scantily 

 wooded districts of the mountain. On the densely wooded eastern 

 and southern sides where there is a thick soil-cap, it is by no means 

 so evident. Here on the western slopes have been carved out deep 

 broad valleys and lofty spurs, the last in their turn furrowed on 

 their flanks, without any apparent sufficient cause. The shallow 

 streams at the bottom of the valleys appear quite incompetent to 

 produce such great erosion ; and doubtless these results are partly 

 due to the action on the crumbling rock-surface of temporary 

 torrents formed during the rains. 



(c) The Northern Slopes of Seatura. — Here within the scantily 



