438 THE GEOLOGY OF THE NEW HEBRIDES, 



iv. The Agglomerates. — At Undine Bay,* outcropping from 

 near sea-level to elevations of about 2000 ft. (Plate xiv.) is a thick 

 series of agglomerates composed of fragments of rock similar to 

 the basic lavas of Man and Nguna. This series appears to 

 overlie the more acid pumice tuffs met with further to the west. 



In some of the gullies where sections of these rocks are obtained, 

 bedding planes varying considerably in dip within short distances 

 can be seen, representing the surface slope of deposition. The 

 rounded volcanic boulders composing the agglomerate were found 

 up to 2 ft. in diameter, and represent a variety of types from 

 that of a basic andesite to a basalt, usually cellular and invariably 

 retaining a certain amount of glass base. 



Crossing the agglomerate beds, generally along the planes of 

 deposition though to a less extent in every possible direction, 

 are very numerous dykes and sills of porphyritic basalt (Sec. 3, §8) 

 measuring up to 30 ft. in thickness. These intrusions must 

 have taken place at a comparatively late period, as they were 

 found intruding the older coral cappings in the vicinity; their 

 injection was probably contemporaneous with activity in the 

 vicinity of Fatmalapa, where a small centre of eruption seems 

 to have been developed synchronously with those of Mau and 

 Nguna. 



V. The Raised Rkefs. — Capping all the formations previously 

 described are beds of coral limestone, probably seldom exceed- 

 ing 50 ft. in thickness, but developed on such an extensive scale 

 as to leave little of the underlying foundation-rocks exposed 

 (see Sec.3, §2). Two of these raised reefs, soniwehat older than 

 the others, cap the agglomerate hills to the south of Undine Bay, 

 and have been intruded as mentioned in the last paragraph. The 

 upper of these can be seen in the photograph (Plate xiv.) at an 

 elevation of over 2000 ft., forming the crowns of the hills. 



Below, at an elevation of 1000 ft. and upwards, is the second 

 development of older reef-limestone, which in the vicinity of 



• See Plate ii. in ' Preliminary Note.' Report A.A.A.S. x. 1904. 



