BY B. SAWYER AND E. C. ANDREWS. 103 



At Namuka, in the Tongan Group, one of us witnessed a 

 similar phenomenon. 



It seems ver}^ probable that the caves of Vatu Leile and Yavau 

 have been formed by processes such as those just described, and 

 that they mark stages in the process of reef-making. 



At Vatu Leile there are unmistakable signs of recent up- 

 heavals, the whole series of elevations (5 in number) being of so 

 recent a date that the line of beach erosion on the cliff which 

 marks the position of stable equilibrium before the elevatory 

 influences came into play has not yet been obliterated. 



Again, above the caves a thin crust of limestone occurs, 

 marking the old reef-platform. Where this old platform ends 

 against the cliff another line of beach erosion exists, and that 

 nearly perfect. It will thus be seen that these large half-marine, 

 half-aerial chambers must have been excavated while the line of 

 beach erosion suffered but very slight alteration, if we assume 

 that seolian agencies have been the prime factors in their 

 formation. 



At Yavau we have a very similar state of things. Here the 

 uplifts are 3 or 4 in number. It is, however, possible that the 

 lines of beach erosion may suggest another method of formation 

 for these caverns. 



In Mango and Thithia the broader outlines of the caverns seem 

 to have been determined by submarine agencies. 



It is impossible to ascertain the exact condition of the cave- 

 walls, as they existed beneath the sea, since secondary deposits of 

 calcareous material have so covered them as to obscure their 

 original shape. 



Stalactites, stalagmites and shawl-like growths do not appear 

 to imply great periods of time, as may be seen by an examination 

 of the most recent of the raised lines of beach erosion on Vatu 

 Leile. This is in places where the cliff overhangs almost entirely 

 obliterated by stalactitic deposits, while in other portions of the 

 island the line of beach erosion is almost as intact as when it rose 

 from the sea. 



