548 Brazilian Corals and Coral Reefs. (September, 
produce a hard coral-like substance. This is one of the most 
important organisms living on the reef at present, and while aid- 
ing to protect it from wear is also building it up. The barnacles 
and worm tubes of the upper portion we have already referred 
to, and we have also stated that over the inner surface there 
seems to be nothing alive. As we enter the many open pools 
and passage ways of the inner margin there is scarcely more to 
be seen. ‘Only here and there does a small mass of coral grow, 
usually a Siderastrazea or a Favia. Seaweeds and delicate tufted 
hydroids and bryozoans hang from the sides of the pools, and a 
few shell-fish and star-fish lie on the sandy bottom. Small, bril- 
liantly-colored fish dart hither and thither, but the life is not what 
we are taught to expect about a coral reef. 
The features we have so far been giving are those of the 
northern section of the reef. Going southward a short distance, 
the elevated outer mass gradually diminishes in size, until it is 
reduced to a slightly raised border along the seaward margin of 
a broad and flat reef. Still farther south the entire lower surface, 
without the raised margin, seems lifted bodily upwards to form a 
high massive wall, like that of an immense fort, flat above and 
perfectly square at the sides. 
Between the points of Pefia and Cruz we find a varied struc- 
ture, generally, however, only a repetition of the forms already 
described. The reef is often two or three times as broad as at 
Jaburú, but near its southern end it becomes very irregular and 
much broken up, existing as,a line of detached reef masses. The 
passage ways through the reef are sometimes mere simple breaks, 
cut as squarely and neatly as though the work of man; at other 
times, however, the edges of the reef bordering them are carried 
obliquely inwards some distance toward the beach, enclosing a 
narrow entrance channel. These inner prolongations, although 
generally low and level, have the same structure as the main reef. 
Within the reef the water is always shallow; frequently the 
bottom lies so high as to be quite exposed at low tide, and it is 
covered nearly everywhere by a thick deposit of coral fragments, 
cemented together by carbonate of lime. The corals are not in 
place but lie heaped together in every conceivable way, as though 
they had been violently broken from the reef at some former 
i e time and thrown inside by the waves. All the commoner forms 
are there, Pa Siderastræa, Orbicella and Mussa being the 
