550 Brazilian Corals and Coral Reefs. [September, 



dead, but are sometimes overgrown by worm tubes and thus 

 become imbedded. 



Here and there, the slaves in procuring limestone, have quar- 

 ried into the low inner part of the reef, and even into the high 

 wall-like portion. Good sections for study are thus formed, and 

 they tell us of what the reef consists. Many large heads of 

 Orbicella, Acanthastraea and Siderastraea stand there exposed in 

 their original positions, and when cut through show their struc- 

 ture to be as open and perfect as though they were still living. 

 With them are many large millepores and nullipores, and all the in- 

 tervening spaces are filled in with a compact calcareous substance. 



Our structure began as a true coral reef, stretching along the 

 submerged rocky ledge. The water was very shallow, however, 

 and the reef soon reached a level above which its corals could 

 not live. Over them nullipores began to grow, but probably 

 while the reef was being raised by other causes than those of 

 growth, large numbers of these dead and partly entombed corals 

 were swept inward by the waves. Nullipores continued to thrive 

 and serpulae came in to aid them, but with these forms we are 

 already familiar. 



Under certain conditions corals begin to grow in scattered 

 patches over the sea bottom, and build up columnar masses which 

 may eventually reach the surface. These columns vary in diam- 

 eter from two or three feet up to several yards ; they are very 

 irregular on top, and covered with living corals. Such structures 

 frequently occur near the shore, generally along the margin of a 

 fringing reef; but their true habitats — where they are best devel- 

 oped — are in the deeper waters of the Abrolhos region, and 

 between there and the city of Bahia. They have also been 

 recorded from Florida and other parts of the world, but on the 

 Brazilian coast they are a much more prominent feature, com- 

 posing nearly all the larger reef patches. 



. As one of these coral pillars approaches the surface of the sea, 

 the tendency to upward growth is necessarily destroyed, and the 

 corals living only at the sides build out a rim about it. A mush- 

 room or umbrella-shaped structure, called by the Brazilians 

 chapeiroes, or big hats, is thus produced. If many such chapei- 

 roes occur near together, their ever enlarging rims finally meet, 

 resulting in the formation of a connected reef surface, supported 

 by many upright pillars underneath. 



Prof. Hartt, in his " Geology of Brazil," already quoted, has 



