34 E. C. ANDREWS, 
Society Islands with the Paumotus, and Tonga, were again 
affected by the revival of the formation of earth waves. 
The movement was vibratory and undulatory. The alge- 
braic sum resulted in pronounced subsidence. 
By this action the groups under discussion were separated 
by sea troughs from the more stable blocks to the west. 
Coral reefs grew upon these sinking areas and formed 
terraces thereon. ‘The vertical distance between any two 
terraces on a given island is a measure of the amount of 
submergence during the particular vibration of undulatory 
movement of the earth wave at that stage. Inasmuch as 
these sinking islands were isolated from the land areas, 
and were formed in clear water, they were not bedded but 
assumed instead an amorphous and dense form showing a 
high content of lime carbonate, without notable admixture 
of foreign material, such as silicates; excepting such organ- 
isms living on the reefs, which secreted silica in their tests 
or shells. | 
During a revival of movement within the later Pleistocene 
the more stable blocks of the western portion of individual 
groups were not affected, but in the eastern islands of the 
groups the axes of uplift appear to have moved slightly 
so much so that the coral reefs which had been formed as 
terraces during submergence, were converted at this later 
stage into elevated terraces mainly of emergence and in a 
minor degree only of erosion. This movement of elevation 
was also vibratory and undulatory, as recorded by the lines 
of marine erosion which occur at variable heights on the 
associated islands, and which mark the positions of stable 
equilibrium during uplift. | 
Vatu Lele has five lines of marine erosion within a ver- 
tical height of 50 feet above sea level, whereas Vata Vara, 
in the same group, possesses several such Jines only, and 
these are distributed within a vertical height of 1030 feet. 
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