V NA SAVU TABLE-LAND 8i 



The massive rocks underlying the agglomerates in the vicinity 

 of Na Savu are aphanitic augite-andesites, differing in important 

 characters from the rocks of the agglomerates. They probably 

 represent ancient lava flows of the Na Savu vent. They are 

 compact (sp. gr. 272 — 276), and display a groundmass formed of 

 a felt of felspar-lathes, averaging -05 or -06 mm. only in length, and 

 in flow-arrangement. That occurring just below the falls is almost 

 aphanitic, but is referred to genus 13, species A, sub-species a, 

 Df the augite-andesites. The rock from the gorge below is of 

 :he same character, but on account of its opaque plagioclase 

 Dhenocrysts it is referred to genus 14, and is described on p. 279. 

 In one place on the plateau a tuff-agglomerate is penetrated 

 l)y veins, a few inches thick, formed apparently of a finely brec- 

 ciated tuff of basic glass fragments in a palagonitic matrix. It is, 

 however, pointed out on p. 340 that they were originally veins of 

 basaltic glass which have been subjected to crushing, and that the 

 palagonite has since been produced. 



In concluding this description of the table-land of Na Savu, it 

 nay be inferred that the source of its basic tuffs and agglomerates 

 is to be found in the same locality ; and probably the original 

 vant is now represented by the hollow extending eastward from 

 tlie falls. With the exception of a large block of silicified coral 

 found in the vicinity of Ndawathumi and of the impure flints of 

 the surface of the plateau, which are described on pages 354, &c,, no 

 d rect testimony of its submarine origin offered itself to me. The 

 pilagonitic characters of the tuffs afford, however, indirect evidence 

 ir this connection ; and indeed the occurrence of submarine tuffs 

 ,,ai d limestones in the vicinity of Tembenindio on its lower northern 

 . sbpes (see page 131), and the existence at elevations of several 

 hi ndred feet above the sea of fossiliferous tuffs and clays in the 

 W ainunu and Ndrandramea districts to the eastward, afford strong 

 pr isumptive evidence that the tuffs and agglomerates of the table- 

 land were deposited under the sea, and I may add in a period 

 su Dsequent to that of the formation of the great basaltic flows of 

 Sc atura and Wainunu. 



