420 THE GEOLOGY OF THE NEW HEBRIDES, 



At Black Sand Bay on the east coast of Malekula, and for 

 some distance to the northward, very large quantities are to be 

 found, highly concentrated within the wash of the weaves and 

 decreasing in richness very rapidly towards the land, w^here it 

 blends with the soil. It consists very largely of magnetite, in 

 addition to which is a varying quantity of pyroxene and felspar; 

 the sand is derived from the decomposition of ash-beds and lavas. 

 Usually on digging down into it alternating bands of a black and 

 of a yellowish-green hue a few inches in thickness can be detected, 

 due to the varying concentration of the magnetite constituent. 

 The grain-size usually averages 0-2 mm., but exceeds this in 

 several localities, as, for example, near the Roman Catholic 

 Mission on the north coast of Aoba, where it averages 2 mm. 

 diam. 



3. Well bedded Miocene tuffs and limestones appearing in the 

 stream a few hundred yards below Bartaleppe. The coarser- 

 grained grey types are largely composed of subangular fragments 

 of pre-existing calcareous rocks averaging 0*5 mm. diam., and fine 

 mineral grains; the binding material is a calcareous cement. 

 Other fine-grained grey types, often much stained along the 

 joints by manganese, are very largely built up of Globigerina 

 tests. 



4. Granular foraminiferal limestone resembling a sandstone 

 in general appearance and of a greyish colour tinged with brown 

 and black spots. It .is composed of a mass of foraminifera 

 (Miocene), pieces of black volcanic glass containing lath-shaped 

 felspars, angular fragments of a yellowish calcareous sedimentary 

 rock, and occasional grains of plagioclase, pyroxene and magnetite. 



5. A grey mineral tuff similar to those of the Wai Bubo in 

 S.W. Santo. The rock is composed of grains of felspar, horn- 

 blende, augite, and magnetite, together wdth numerous fragments 

 of andesite lavas, and much decomposed reddish-stained opaque 

 material resembling palagonite. This rock is, for the most part, 

 barren of organic remains, though the discovery in it of an 

 echinoderm spine served to settle its submarine origin. 



