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



while the bed of the Wainikoroiluva is 270 feet below the same 

 point. 



I have very little doubt that, originally, the Waidina and the 

 Navua formed one stream. This may have risen somewhere near 

 the present town of Waivaka, and flowed W.S.W. to the sea; or 

 it may have risen near the source of the present Navua, and 

 flowed E.N.E. to join the ancestor of the Rewa. Of the alterna- 

 tives, the latter is the more probable. The disturbance in 

 stream-arrangement was almost certainly due to heavy faulting 

 along the line of the Medrausucu Range, and along the course of 

 the Wainikoroiluva and lower Navua, leaving the intervening 

 area as a "horst." 



No detailed examination was made of the Waimanu Valley. 

 The river has a remarkably uniform general direction a little 

 north of east, parallel to the Navua- Waidina line just referred to 

 and at right angles to the fault-lines which determine the 

 " horst." Like the Wainivalau and Waidina, it has the 

 character of an antecedent stream, crossing the Medrausucu 

 Range (here rather indetinitej by means of a picturesque water- 

 gap. This gap is a very conspicuous feature when viewed from 

 Uvuuvunidavui. I crossed the stream at a point between 

 Vesari and Nabukaluka, and there noted the important fact that 

 granites form a large part of the gravels. From the small size 

 and complete rounding of the pebbles, we see that the outcrops 

 of granite in situ must, probably, be near the head of the 

 stream. This brings the granite area considerably further south 

 than it has ever been observed before. I was informed by 

 natives that it is possible to canoe upstream for some distance 

 from its confluence with the Rewa, but then its coarse becomes 

 broken up by impassable rapids. These continue for some 

 distance above the point where I crossed it, but then the valley 

 widens out again and the river becomes navigable. This agrees 

 with all the other topographic evidences which point to a very 

 recent origin of the Medrausucu Range. 



Summary of Section iii. — The Waidina and Wai- 

 manu Valleys are about parallel to one another, and at right angles 



