54-8 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 Siderastraea 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 fiat 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 

 Jaburu, 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 

 time and thrown inside by the waves. All the commoner forms 

 are there, Millepora, Siderastraea, Orbicella and Mussa being the 



