30 bulletin: museum of comparative zoology. 



these lies an immense block 100 feet long and some 30 feet thick. This 

 is a recent fall, while all around and below it are thousands of blocks 

 with isolated specimens as much as 100 tons weight. At Thithia there 

 is an exposure of limestone preserving a beautiful slope of from 50° to 

 60° for a couple of miles. In one place, however, this continuity is 

 broken. A huge block of some 20,000 tons (150 X 50 X 60 feet) has 

 slipped down slightly, and should it fall over would expose a cliff over 

 100 feet in height. The precipices occupying the upper 300 feet of 

 Vatu Vara may have been formed similarly. 



Perhaps, however, the majority of cliffs represent originally steep 

 submarine slopes. Again, on the western side of Vatu Leile the cliffs, 

 100 feet in height, persist for miles and are quite vertical (Plates 

 28, 30, 31). Yet on these cliffs are to be found no less than four 

 well-defined lines of old beach-erosion. Therefore these cliffs must 

 have been submarine. There has, however, been a certain period of 

 quiescence since the last uplift, for a modern fringing reef has formed 

 outside of the cliffs. The next uplift would give a terrace structure 

 to Vatu Leile. Similar evidence is given from Yathata and Vatu 

 Vara (Plates 25, 27). In many cases there are no outliers indicating 

 an erosion so long continued as to eat back the " sugar-loaves " into 

 enormous 400 feet cliffs and to have got rid of the vast accumula- 

 tions of debris that would result from such a dismantlement of the 

 gigantic vertical exposures. For it must not be forgotten that many 

 high cliffs gather comparatively little limestone debris at their feet. 

 In some instances the cliffs abut directly onto a sand flat with no 

 intervening talus to lessen the angle of ascent. 



The Nature, Origin, and Age of the Elevated Limestones. 



Tuvuthd (Plate 3, Figs. 3, 4) furnishes positive evidence of four 

 elevations as terraces, occurring every 200 feet. Yathata is equally 

 characterized by its terraced appearance. Vatu Vara presents steep 

 acclivities and very poorly developed terraces. Vatu Leile empha- 

 sizes the short and frequent intermittent uplift, while Mango, Kam- 

 bara, Mba Vatu point to long-protracted periods of stable equilibrium. 



Of all the islands in the Lau Group, none perhaps are more remark- 

 able than Tuvutha,, Vatu Vara, and Yathata. They are closely allied 

 in structure, as regards height and traces of elevations. Tuvutha is, 

 perhaps, the most remarkable of all. Its summit is represented by a 

 curious peak (Plate 3, Figs. 3, 4), 800 feet above the sea, and rising 150 



