GEOLOGICAL OBSERVATIONS IN FIJI. 77 



Munia. 



Munia is the one remaining member of the Exploring group not 

 described. It differs from all the others in that it has no limestone 

 in its composition. The island belongs to the last or basaltic period 

 of volcanic acti\'ity and is believed to have been built on an eroded 

 bank of elevated coralliferous limestone and volcanic rocks. 



Munia is elliptical in shape, its main axis directed northeast-south- 

 west. It is composed of interbedded layers of agglomerate and ash 

 which have been deeply eroded. A central ridge, 950 feet high at its 

 simimit and flanked by retreating cliffs, runs northeast through the 

 island. The ash-beds exposed in the face of the eastern cliffs dip 20° 

 to 30° E. In the rainy season land-slides from the cliffs are not 

 infrequent. The slopes at the northeastern side of the island, are 

 gentle and follow the initial dip of the volcanic rocks. At the extreme 

 northeastern end of the island the deposits are nearly all ash. 



On the southwestern side of the island, a depression appears to 

 represent an old crater. Along its inner slopes the dips of the volcanic 

 beds are quaquaversal and slope in every direction except to the 

 north and northwest, where the crater walls have been destroyed. 

 In describing Susui, an adjacent island, it was stated that the eastern 

 end of that island is formed of agglomerates which dip westward and 

 had their origin in Munia. Remnants of the original western slopes 

 of Munia are also to be found as dismembered islets about the lagoon. 

 The following map and cross section (Figure 38) illustrate the type of 

 land form developed in Munia. The eastern slopes are clearly ero- 

 sional forms but probably the western side of the island was destroyed 

 by explosive violence, merely supplemented by erosion. 



The volcanic debris, erupted from the crater in Munia and now 

 composing the eastern part of Susui, overlies elevated limestone. For 

 this reason Munia has been placed in the recent or basaltic period of 

 eruptivity of the Exploring group. The recency of the volcanic 

 action is attested not only by the topography but also by the slight 

 lateritization of the basaltic agglomerates. While lateritization has 

 extended to a depth of 20 to 30 feet in the andesitic rocks of Vanua 

 IVIbalavu, the maximum observed depth in Munia is but 2 or 3 feet. 



The shore-line of Munia is little indented and gives slight indication 

 of recent submergence. On the contrary, a recent uplift is suggested 

 by the fact that some floors of the mature valleys are trenched by 

 small streams to depths of 5 to 8 feet. 



The formation of a volcano on an eroded mass of elevated limestone 



