DEVELOPMENT OF EEEES. 
299 
portion of tlie lagoon of an atoll, and the inner portions of 
the lagoon channel of a barrier reef, are more recently pro- 
duced than any other portion of the area of such reefs.’ 
The smallness of the outer corals is * only to be explained 
on the hypothesis that the reef has gradually grown out- 
wards as from a centre, and quite independently of any 
movement of subsidence.’ Further, the low coral lime- 
stone cliffs, which not seldom hack the present reef flats, 
are probably lines of erosion, indicative of an epoch an- 
terior to the formation of the shore reefs, when these cliffs 
were washed by the sea. The disposition both of the 
vegetation and of the humus on the wooded islets shows 
that the lee side of such an islet is its oldest portion, and 
its weather side is its growing margin. 
Illustrative of the question of the removal of dead coral 
by solution, cases are mentioned of masses of madrepora 
and porites several feet across, the centres of which were 
dead and were depressed a few inches below the living ex- 
terior. During the bright sunlight the increased tempera- 
ture 1 of the sea water covering the reef flats probably assists 
in the solution of the dead coral ; moreover its destruction 
by organisms, to which other authors have called attention, 
must not be overlooked. Holothurians and echinids play 
an important part in this respect. 
The author concludes by stating that the calcareous 
sand and gravel which strew the outer slopes below the 
zone of living coral are largely composed of reef debris, of 
the tests of Orbitolites complanata and 0. heterostegina, 
of the joints of the calcareous alga Halimeda opuntia and 
of nullipores. Of these the foraminifera were found living 
between 2 feet and 75 fathoms ; the alga does not appear 
to live below 10 fathoms. At greater depths than 100 
fathoms the sea bottom consists generally of volcanic mud 
1 About 16° F. higher than the open sea where the water was onty 
S or 4 inches deep, and 8 higher where it was a foot deep. 
