174 A NATURALIST IN THE PACIFIC chap. 



The ascent is very gradual for the first one and a half miles, 

 when an elevation of 2,600 feet is attained. From here one ascends 

 the steep-sided peak of Mbatini, which rises some 700 or 800 feet 

 from the ridge. As one nears the highest point the crest becomes 

 very narrow, between 1 5 and 20 feet across ; and on either side 

 there is apparently a drop of several hundred feet. The actual 

 peak, which is bare and rocky, is yet narrower ; and when it is 

 enveloped in dense mist as it was in my instance, it is not a very 

 secure situation for a geologist. It is highly magnetic, as is the 

 case with most of the other bare peaks of the island. The rocks 

 exposed in the upper 500 feet, that is, in the peak proper, are 

 highly altered semi-vitreous, but extensively weathered, hypers- 

 thene-augite-andesites which are referred to genus i of that sub- 

 class. Much of the glassy groundmass is replaced by viridite, 

 silica, calcite, &c. Less altered specimens display in a brown 

 opaque glass small felspar-lathes averaging less than "i mm. in 

 length. They exhibit phenocrysts of rhombic pyroxene and augite, 

 the first prevailing. 



I did not climb Soro-levu, the other of the twin-peaks. Its 

 ascent should be made either from Nukumbolo or from one of the 

 villages on the neighbouring shore of Natewa Bay. My acquaint- 

 ance with Mbatini, although very incomplete, enables me however 

 to point out a few of its general features. As remarked before, 

 there is a general uniformity in the type of its rocks. The olivine- 

 basalts and basaltic andesites, prevailing in the Koro-tini Range, 

 are not here represented, nor are the dacites or acid andesites to 

 be found. The characteristic rocks are more or less altered 

 hypersthene-augite-andesites having a specific gravity in the least 

 altered and least vitreous condition of about 27 ; whilst the average 

 length of the felspar-lathes is always less than "i mm. The same 

 type prevails from the upper part of the Lovo valley to the summit 

 of Mbatini ; but it is only in the actual peak that these rocks 

 show much glass in the groundmass, though extensively affected 

 by alteration. Neither tuffs nor agglomerates came under my 

 notice ; but they might be expected to occur on the other slopes. 

 I am inclined to regard this mountain-ridge as a huge dyke-like 

 mass or sill, representing the remains of a volcanic vent that has 

 been subjected at different periods to marine-erosion and in later 

 ages to sub-aerial denudation. 



