c;K()L()(;i( AL ohskrvatiuns in ii.ii. 



17 



within the Yasawa <;r()iii) huniiin' witli their asli the cro !»> 1 Hmcstoiics 

 of that area. 



4. The volcanic cones were then eroded to suh-maturity and in 

 comparatiAcly recent times ha\'e been submerged. 



"). The uphft of the Xanch river gravels and of the coastal series 

 near the mouth of tlie Singatoka river in southwestern Viti Levu 

 occurred (hn-ing the recent submergence of the Yasawa islands. 



There has been, therefore, a slight tilting of the lagoon in recent 

 times towards the northwest, but the lagoon and its bordering reef 

 did not originate with this movement. It is a much older feature. 



Ya.mwa Group. 



Lying along the western edge of the lagoon which has just been 

 described is a series of islands the southern members of which are 

 known as the Malolo group, and the northern, as the Yasawa group. 

 Most of these islands are composed of andesitic rocks, sub-maturely 

 eroded. Their coastal outlines offer some of the best examples of 

 embayed topograph}' to be seen in Fiji. 



A few of the islands contain elevated limestones, the rocks of spe- 

 cial importance in the present investigation. Viwa, the most westerly 

 island of the Fiji Archipelago, is low, fiat, and composed of upraised 

 coralliferous limestone with a central hill about 20 feet in height. 

 Lacking means of visiting this island, the writer devoted his time to 

 the two other islands showing coralliferous limestone, namely Nathula 

 and Yasawa-i-lau. 



Xathula, one of the northern islands of the Yasawa group, has a 

 rough interior of elevated peaks 

 bounded by sheer cliffs. Its 

 coast-line is very irregular and 

 is fronted by numerous dis- 

 membered islets. At its ex- 

 treme northern end, a small 

 area of sandy limestone was 

 found to contain pelecypod 

 shells and coral, mingled with 

 blown, angular bits of andesitic 

 glass and augite crystals. The 

 area forms a point not over an 

 acre in extent. The limestone 

 has a dip of 25° E. and is much brecciated, owing to the intrusion of 

 a fine grained dike of andesite (Figure 5). 



Figure .5. Cross-section of the 

 Northern End of Nathula, Yasawa 

 Group. 



White — intrusive basalt. Dashed 

 — elevated limestone. Dotted — 

 sandy flats. 



