192 DISTRIBUTION OF CORAL-REEFS. Ch. VI 
longed by numerous reefs to a point 2,000 miles dis- 
tant from Hawaii. The south-eastern end of this long 
line is one of elevation and of volcanic activity; 
whereas the north-western end, judging from the 
structure of the reefs, though these are imperfectly 
known, is one of subsidence. 1 So that here we ap- 
parently have opposite movements in progress towards 
the two extremities of the same long line. The com- 
monest case seems to be a tendency to alternation 
between the areas of subsidence and elevation, as 
if the sinking of one had counterbalanced the rising 
of another. 
The existence in many parts of the world of lofty 
table-land, proves that large surfaces have been upraised 
in mass to a great height above the level of the sea ; 
although in almost every country the highest points 
consist of upturned strata; or of erupted matter : and 
from the wide spaces over which atolls are scattered, 
although not one pinnacle of land now remains above 
the level of the sea, we may conclude that immense 
areas have subsided to an amount sufficient to bury not 
only any formerly existing lofty table-land, but even the 
heights formed by fractured strata and erupted matter. 
The effects left on the land by the later elevatory 
movements, namely, successively rising cliffs, succes- 
sive lines of erosion, and great beds of shells and 
pebbles, all requiring time for their production, prove 
that these movements have been extremely slow. And 
' Dana, Corals and Coral Islands, pp. 307, 355. See also mj 
Appendix. 
