122 A NATURALIST IN THE PACIFIC chap. 



ing the north slopes of the range, basaltic andesites, often doleritic 

 in texture and referred to genus i of the augite-andesites, are usually 

 found as far as the summit 1,200 to 1,300 feet above the sea. On 

 descending the south slopes one finds coarse and fine palagonite- 

 tuffs and clays at 900 to 1,100 feet up, similar to those prevailing near 

 the sea-border. They are probably submarine, but my specimens 

 are weathered and give no effervescence with an acid. In the bed of 

 the river above Vatu-vono, about 400 feet above the sea, there 

 occurs in position an aphanitic augite-andesite (spec. grav. 277), 

 referred to genus 16, species A ; whilst blocks of a coarser grained 

 basaltic andesite lie loose in the stream. 



In my traverse across the range from Valeni to Nareilangi I 

 noticed about a mile from Valeni and not much over 100 feet 

 above the sea an agglomerate formed of blocks of an altered acid 

 andesite possessing a micro-felsitic groundmass and showing micro- 

 porphyritic rhombic pyroxene with dark alteration borders (spec, 

 grav. 2"5). It is distinct from the Na Raro rocks ; and its presence 

 in an agglomerate seems to indicate the vicinity of some old acid 

 andesite peak buried beneath later basic eruptive products. 

 Ascending the south slopes of the range, I found decomposing 

 basaltic andesites and basic tuffs, the prevailing rocks up to an 

 elevation of 1,300 feet ; but in one locality (800 feet) occurred large 

 masses of what seemed to be a disintegrating dacitic rock penetrated 

 by quartz veins less than an inch thick. An aphanitic augite-andesite, 

 of a somewhat exceptional character (spec. grav. 2'63), was displayed 

 at the top of the ridge, 1,500 feet above the sea.^ Basic rocks were 

 exposed in the spur running northward on the east side of Na 

 Raro. 



The Sea-border Extending East from the Yanawai 

 River to the Lango-lango River. — In this district is in- 

 cluded the area between the foot of the slopes of the Tavia Ranges 

 and the shores of Savu-savu Bay. This undulating country, two 

 to three miles in breadth, does not attain a greater elevation inland 

 than 300 or 400 feet. Fine and coarse palagonite-tuffs, some of 

 ihem with the texture of sandstone, are the characteristic rocks. 

 They at times contain a little lime and probably a few tests of 

 foraminifera. The palagonitised glass is often vacuolar, the vacuoles 

 being filled with the same material. In places where they are well 

 displayed these tuffs generally show bedding, as in a hill-slope just 

 east of Vuni-evu-evu, where there are fine and coarse tuffs inter- 



' It displays in the groundmass augite prisms in flow-arrangement, and is 

 referred to genus 20 of the augite-andesites. 



