1 86 A NATURALIST IN THE PACIFIC chap. 



When viewed from the top of the hills behind Valanga, this 

 mountainous range has a very imposing appearance. On the 

 south side it rises precipitously to the summit, but the northern 

 slopes below an elevation of i,8oo or 1,900 feet descend with a very 

 easy gradient for i^ or 2 miles into the valley of the river Ndreke- 

 ni-wai. In the first case the average angle of the slope would be 

 from 15 to 20 degrees and in places often more ; whilst in the 

 second case the average inclination would be about 7 degrees. 

 The contrast between the two sides of the range is very striking" 

 and one ought, I think, to find a parallel in the broken-down rim 

 of a large crater with a gentle outer slope and a precipitous inner 

 face. When descending recently the outer slope of Monte Somma, 

 the ancient Vesuvian vent, I found reproduced some of the features. 

 of the northern slope of Mariko. The tuffs and agglomerate-tuffs 

 that cover their outer flanks are in both mountains deeply scored 

 by the gorges and ravines worn by the torrents. After the de- 

 scription of the geological structure of the Mariko Range, we shall 

 perhaps be in a better position to consider this question ; but until 

 a proper survey of the region has been made it will not be possible 

 to give a final answer. There are also many other uncertainties 

 which would be removed by the accurate mapping of the district, 

 such for instance as the mode of connection between the Mariko 

 and Valanga Ranges. 



The highest peak of the Mariko Range is irregularly square- 

 topped and is only a few paces across. It has a soil-cap and 

 supports small trees and shrubs, whilst there is a precipitous rocky 

 face on the east and south. Like most of the other lofty peaks of 

 the island it is magnetic, and as remarked on page 368, it markedly 

 deflects the compass-needle. 



I made two ascents of this mountain from Vunimbua, one to 

 the highest peak (2,890 feet), and the other across the range to 

 Nukumbolo at a point half a mile or more to the west of the 

 summit, where its elevation is 2,200 feet. Basic agglomerates and 

 agglomerate-tuffs prevail on both the slopes up to 1,800 or 2,000 

 feet, the blocks being composed of a dark semi-vitreous basic 

 andesite referred to the hypersthene-augite sub-class with specific 

 gravity 275. It contains much glass in the groundmass, and since 

 the pyroxene of the groundmass is prismatic, this rock belongs to 

 the prismatic sub-order described on page 289. Ordinary basic 

 tuffs are also well represented on the north flank. On the south or 

 precipitous side they are usually more or less altered. Here, for 

 instance, they may take the form of a hard breccia-tuff containing 



