550 Brazilian Corals and Coral Reefs. [September, 
dad, 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, Acanthastrzea and Siderastrzea 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- 
terveniny 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 serpulz 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- 
rões occur near together, their ever enlarging rims finally meet, 
resulting in the formation of a connected reef surface, supported 
by many upright pillars underneath. a 
Prof. Hartt, in his “Geology of Brazil,” already quoted, has 
