250 W. M. Davis — Shaler Memorial Study of Coral Beef s. 



sediments, but allowed for a time while the delta-forming 

 river mouthed some distance away ; and that emergence placed 

 the delta, with its little local reefs, in an elevated position. 

 Since then, mature valleys have been eroded in the high-stand- 

 ing delta ; the valleys are now embayed, and the embayments 

 are more or less filled by sea-level deltas and mangrove swamps, 

 as may be seen at Walu bay, for that little cove and its several 

 neighbors are nothing more than drowned- valley embayments; 

 hence emergence has lately been followed by a smaller 

 submergence ; it is presumably in association with this latest 

 submergence that the present barrier reef of Yiti Levu has 

 been built up. The broad, now delta-filled valleys of the 

 larger rivers were probably excavated or re-excavated during 

 the last emergence, while the creeks were cutting small valleys ; 

 and the broad delta-plains of the large rivers, extensively 

 cultivated in sugar-cane plantations, were formed during and 

 since the last submergence. 



It was possible for me to examine only two of the larger 

 elevated reefs in the Fiji group — those of Yanua Mbalavu 

 and of Mango islands — in sufficient detail to discover their 

 structure and to infer their history. Only the elevated reef 

 of Yanua Mbalavu will be here described. Its limestones were 

 usually so weathered or incrusted as to conceal their bedding, 

 but at two points in a bay, block 7, fig. 7, about a quarter of a 

 mile apart, and several hundred feet below the hilltops of the 

 sharply dissected mass, well-defined horizontal stratification was 

 seen, such as must occur in the lagoon deposits of an up-grow- 

 ing reef around a sinking island (see sector M, fig. 9), but 

 such as could not be formed in the slanting talus beds of an 

 out-growing reef around a still-standing island. Of greater 

 dimensions and of greater importance than these details 

 was the unconformable relation between the limestones of the 

 uplifted reefs and their volcanic foundation, as seen in Yanua 

 Mbalavu, and as represented in the foreground section of fig. 7. 

 This relation was not attested by the discovery of actual 

 surfaces of contact between the two structures, which would 

 be difficult to find and to follow under deep-weathered soils 

 covered by dense growth of reeds or trees, but was determined 

 only by the resemblance of the general line of contact, as seen 

 from a little distance away, to the profile of the uncovered 

 slopes of the volcanic mass in other parts of the island. 

 The uncovered slopes have evidently suffered long-continued 

 erosion, for they exhibit mature or subdued spur-and-valley 

 forms of insequent branching arrangement, such as only long- 

 continued erosion can produce in volcanic masses ; hence 

 the similar volcanic slopes under the limestones of the uplifted 

 reefs were also believed to have suffered erosion before the 



