446 THE GEOLOGY OF THE NEW HEBRIDES, 



Nguna, Mau and Pele (Plates xv., xvi. fig.l, xvi. fig. 2) are 

 built up of basic lavas (Sec. 3, §7) and call for no special descrip- 

 tion. One point perhaps worthy of note is revealed on the north- 

 east coast of Pele, where part of the old crater-lip has been 

 broken down, revealing beds many feet in thickness of a fine- 

 grained volcanic ash apparently developed under water and later 

 overlaid by further flows of lava. 



Sec. 2. DETAILED GEOLOGY OF SOUTH-WEST SANTO.* 



i. The Earlier Volcanic Serie s. — The oldest 

 rocks met with in Santo are thick beds of agglomerates and 

 tuffaceous rocks developed in the Puria Etsa District on the west 

 coast of Santo. In this locality they are at least 400 ft. thick 

 (above sea-level), built up of fragments of andesitic lavas largely 

 glassy. They are of a greenish-grey colour, due to the develop- 

 ment of much chlorite, which gives them a decidedly older 

 appearance than the more recent agglomerates of the Wai Bubo 

 and La La Vura. Below they are coarsest, much crossed by 

 veins, often several inches thick, of white to greenish secondary 

 minerals resembling zoisite in physical properties; above they are 

 much finer and split up readily along numerous cleavage direc- 

 tions until reduced to the smallest fragments. 



As regards age, they are no doubt early Miocene, for they 

 appear to pass up regularly into the Lepidocyclina-Lithothamnion 

 limestone above, f Thick beds of agglomerate observed out- 

 cropping in the cliffs along the coast southward from Sauri'i to 

 C. Babana are no doubt referable to this same series. 



ii. Miocene Lepidocyclina-Lithothamnion 

 Series . — These beds occupy large areas in south-west Santo, 

 where they are highly tilted and intruded by andesites of the 

 later volcanic series. In their lower portions they are fine- 

 grained dark grey tuffaceous rocks containing occasional radiolaria 



* Refer to Plate xxix. for map. 

 t A more thorough examination of these beds is desirable, as on account 

 of faulting the evidence obtained of their relative age was not altogether 

 satisfactory. 



