OBJECTIONS TO THE THEORY OF SUBSIDENCE. 303 
temperature than the outer, with injury to many species, and, 
at lowest tides, may become destructively overheated by the 
midday sun, as many a plantation of corals with dead tops 
for a foot or more bears evidence. In the smallest atolls, 
the lagoons are liable also to alternations of excessive saltness 
from evaporation and excessive freshness from rains, and con- 
sequently no corals can grow inside, though still flourishing 
well in the shallow sea about the outer reef. The above are 
the facts, not the suggestions of theory. __ 
j. We read: “So great is the destructive and transport- 
ing influence of the sea under the combined or antagonistic 
working of tides, currents, and wind-waves that the whole ! 
mass of the reef, as well as the flats and shoals inside, may 
be said to be in more or less active movement.’* ‘This 
description of the Tortugas reefs is not applicable to the 
atolls of the Pacific nor to the Tortugas. Notwithstanding 
the testimony of Captain Beechey and others about occa- 
sional catastrophes — which are mostly catastrophes to the ~ 
islets and banks within the lagoons—I was led to look 
upon a coral island as one of the most stable of structures. 
Through the wind-made and tidal movements, the loose sands 
are drifted along the shores and over the reef; edges of the 
reef are broken off in gales or by earthquake waves; and 
occasionally a mushroom islet in the lagoon, where growing 
corals are not compacted by wave-action, is overthrown by 
the same means; but beyond this. the structure is singularly 
defiant of the encroaching waters. Earthquakes may bring 
devastation ; and so they may to other lands. 
5. Lagoon-basins made by caving in. — Mr. Fewkes has 
suggested” that the lagoon-basin of the Bermudas may have 
1 Dr. Geikie’s Address, p. 23. 
2 Fewkes, Proceedings of the Boston Society of Natural History, 1888, p. 518. 
