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, 

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

 the same character, but on account of its opaque plagioclase 

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



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

 by 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 

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

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

 vent is now represented by the hollow extending eastward from 

 the 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 

 direct testimony of its submarine origin offered itself to me. The 

 palagonitic characters of the tuffs afford, however, indirect evidence 

 in this connection ; and indeed the occurrence of submarine tuffs 

 and limestones in the vicinity of Tembenindio on its lower northern 

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

 hundred feet above the sea of fossiliferous tuffs and clays in the 

 Wainunu and Ndrandramea districts to the eastward, afford strong 

 presumptive evidence that the tuffs and agglomerates of the table- 

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

 subsequent to that of the formation of the great basaltic flows of 

 Seatura and Wainunu. 



