30 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
these lies an immense block 190 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 débris 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 débris at their feet. 
In some instances the cliffs abut directly onto a sand flat with no 
intervening talus to lessen the angle of ascent. 
Tae Nature, Origin, AND AGE OF THE ELEVATED LIMESTONES. 
Tuvuthé (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 Tuvuthé, 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 
