BY W. G. WOOLNOUGII. 443 



The water-gaps mentioned above are not the only ones developed 

 in the range. Between Ucikavukavu and Nariko there is another 

 well marked one. It is not, however, occupied by a considerable 

 stream. Close to Serea there enters the Wainimala Valley, a very 

 considerable tributary valley whose bed is occupied b}'' a long 

 lagoon known as the Waieliu or " Former River." This heads 

 towards the gap above-mentioned, and I have no doubt that we 

 are dealing here with an instance of river-capture occurring 

 within historic time. The '• pirate " was certainly one of the 

 headwater streams of the Wainivalau, possibly the Waisomo. 

 That this is the case is rendered likely by the large volume of the 

 Wainivalau in proportion to the size of its gorge, as compared 

 with other rivers. 



In addition to the main rivers crossing the line of this range, 

 there are numerous smaller streams rising in it which have cut 

 more or less deep notches, such as the Waibowa, rising just to 

 the south of Nabukelevu, Waicevu north of the Wainivalau, 

 Wainimase south of Serea, and several other still smaller creeks. 



In the bed of the Waibowa pebbles of granite occur, but in 

 the other minor streams crossed no such granitic material was 

 observed. Pebbles of jointed and saussuritized trachyte, exactly 

 similar to that described later, occur, thus showing that fairly 

 ancient rocks occur within the reach of the east-flowing creeks. 



The very great geological importance of this range of mountains 

 will appear later. 



Summary of Section i i. — The Medrausucu Range is a 

 remarkable, linear, wall-like range of volcanic mountains stretch- 

 ing N.N.W.-S.S.E. a little to the west of the meridian of Suva. 

 It is crossed by numerous large rivers which have cut great 

 water-gaps in it, and are certainly antecedent streams. There is 

 at least one important " air-gap," and it is highly probable that 

 the river-capture originating this feature took place within 

 historic time. The smaller streams are busily engaged notching 

 the divide. All the topography suggests extreme youth. All 

 the larger, and some of tlie smaller, streams have reached the 



