BY W. G. WOOLNOUGH. 471 



elevation. It is certain that it was a differential movement. 

 The levels of the highest beds of soapstone and of the basal con- 

 glomerates of the newer series agree in pointing to a general tilt 

 (towards the south-east. 



River -development points to the same conclusion, since 

 the three great river-systems of the Eewa, the Navua, and the 

 Sigatoka have markedly asymmetrical drainage- trees, drawing 

 their waters almost entirely from the northern and western 

 portions of their basins. The exceptions to this rule, which are 

 most marked in the case of the Sigatoka, are believed to be 

 explicable as a result of river-piracy on a large scale. The 

 Sigatoka has probably been robbed by the Ba, but has enriched 

 itself at the expense of the Wainimala and probably of the 

 Navua. 



It is possible that the original tilt was towards the E.N.E., 

 but more probably the marked trend of several of the chief 

 streams in that direction has been determined as a result of the 

 faulting explained above. It will be seen that the rivers have a 

 marked tendency to a rectangular arrangement along general 

 E.N.E.-W.S.W., and N.N.W.-S.S.E. lines. It is believed that 

 this tendency has been imposed upon them by block-faulting of 

 the land. The suggestion is made that the upper Navua and 

 Waidina Valleys were at one time continuous, but have been 

 cut off by the fault along the Nalumbu-Nabui Range. 



The rivers are all in a condition of 3^outhfulness. They are 

 for the most part still engaged in sinking deep narrow canons in 

 the surfaces of otherwise level plateaux. In the case of the 

 Navua River the drainage-system is so immature that its 

 tributaries do not meet it at grade, and the smaller ones form 

 veritable hanging valleys. This immaturity is partly due to the 

 hardness of the rocks through which the beds have to be sunk, 

 as compared with those in the Rewa and Sigatoka Valleys. Both 

 the latter streams have progressed considerably towards maturity, 

 as the "falls-line" on the Rewa has receded a very long way, and 

 the stream has, within the present cycle, built a large delta. 

 36 



