456 TIIK GKOLOGY OF THE NEW HEBRIDES, 



No dolomites were observed, though some of the beds, 'no 

 doubt, run high in magnesia, as contraction cracks are observable 

 in some of the sections. 



Similar beds have now been traced from Europe by way of 

 Arabia, the East Indies, and swinging round the continent of 

 Australia they appear along the north coast of New Guinea, and 

 finally in the New Hebrides. 



iv. Mineral Tuffs compare with specimens from the 

 Wai Bubo a few hundred yards above the ford, where they 

 overlie the Miocene limestones uncomformably. 



They vary in colour through shades of grey, usually dark grey. 

 The rock is compact and hard, and is composed of fine grains of 

 mineral matter and tin}^ particles of lava. In the hand-specimen 

 it is readily distinguished from a volcanic rock by its rough 

 fracture. Bedding planes are as a rule not well marked, though 

 often indicated by dark streaks where magnetite grains are more 

 numerous Under the microscope, however, a rough differentiation 

 of the particles into coarser and finer bands is apparent The 

 constituent grains are angular to subangular, and vary in size 

 from 2 mm. to 0'03 mm. The constituents stated in order of 

 abundance ave -.- — Plai^ioclase abundant and much decomposed; 

 Vohanic glass usuall}^ dusty, sometimes palagonitised; Hornblende 

 light yellowish-green; Pjjroxene, faintly coloured augite; Magnetite 

 relatively exceptionally abundant. Organically derived calcium 

 carbonate is almost entirely absent, though occasional Globigerina 

 tests and, less frequently, shells of tiny gastropods have been 

 noted, attesting to its submarine origin. 



5. Perlitic hypersthene andesite glass. 



Local i ty. — Embedded in the hypersthene andesite pumice 

 tuffs 40 ft. above sea-level at the south-west end of Leleppa 

 Island. In the coarse tuffs near the mouth of the cave fragments 

 of this glass are fairly common up to 10 cm. diameter; they are 

 usually more or less rounded, and are often faced in one or several 

 directions as if roughly polished. On the mainland, in the 

 neighbourhood of the Ai Stream, embedded in these tuffs were 



