444 A CONTRIBUTION TO THE GEOLOGY OF VITI LEVU, FIJI, 



foundation of ancient rocks, in part plutonic, lying below the 

 volcanic material which builds the bulk of the range. 



iii. — Upper Waidina and Waimanu Rivers. 



A journey up the Waidina Valley has already been described,* 

 and very little need be added here. The Great Dyke of Devo 

 (Plate xxiii., fig. 4 of my former paper) bears nearly north and 

 south,! and therefore about parallel to the general trend of the 

 Medrausucu Range, on whose western flanks it occurs. It has a 

 distinct underlie to the west. 



The general direction of the Waidina Valley is about E.N.E. 

 and W.S.W., that is at right angles to the line of weakness 

 suggested by the trend of the Medrausucu Range. The valley 

 is bounded on the south by a range of hills which have the 

 appearance of a line of denuded volcanoes. It is a very common 

 feature in orogenic processes that lines of weakness develop in 

 the form of a nearly rectangular network; the case under discus- 

 sion seems to conform to this general law. Another line of hills, 

 in approximate parallelism with the river-valley, occurs on its 

 northern side, in its upper course. 



I stated in my former description of the Waidina Valley that 

 the hot spring at Naseuvou rises through solid quartz diorite.| 

 This statement has to be corrected. The rock is really jointed 

 andesite, the mistake having been caused by a transposition of 

 specimens. 



A small tributary, the Waimanu, enters the main stream on 

 its left bank, just above the town of Nasirotu, and brings down 

 abundant large boulders of quartz diorite, which rock must, 

 therefore, occur in situ at no great distance to the north. 



I ascertained that the Wainavadu, in which abundant and very 

 large boulders of quartz diorite occur, rises beyond the north- 



* Former paper, p. 465. 

 t Compass bearings in the volcanic parts of the island are often quite 

 unreliable on account of the extraordinary local deviations. 

 X Former paper, p,468. 



