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MR. J. J. LISTER ON THE GEOLOGr 



I was led to visit A'a by seeing its depressed interior from the top 

 of Mo'unga Lafa. From that position the neighbouring island 

 Laiigito 0, to the west of A'a, which rises to about the same height, 

 appeared to have a similar depression in it. Unfortunately I had 

 no opportunity of visiting this island. 



Fig. 4. — Slcetcli of the contour of the island of A^a ( Vavau Group). 



The numbei'S indicate heights, in feet, above the sea. 



The summit of the three-storied hill Talau, near Neiafu, presents 

 similar features. Here, too, a high margin surrounds a central 

 depression, but the margin is complete for only three quarters of a 

 ring. For the other quarter the level of the margin descends to 

 that of the interior. 



The accompanying rough map of the summit of the hill shows 



Yu 



5. — Sketch of the contour of the summit of Talau ( Vavau 

 Group), Tonga Islands. 



The numbers indicate heights, in feet, above the sea. 



the contour. From this it is seen that the bottom of the depression 

 lies some 40 to 50 feet below the higher part of the margin. 



