1879] Brazilian Corals ani Coral Reefs. 547 



Almost everywhere along the inner edge, but more commonly at 

 the ends of the reef and about the openings through it, we find 

 many outlying masses which are often partly continuous with the 

 low, inner surface, but more frequently quite detached. They 

 attain all heights up to that of the lower surface, but never reach 

 above it ; the average depth of water around them is between 

 three and four feet. The outliers on the outside of the reef are 

 merely low, ragged, angular projections from the reef itself, and 

 are never much exposed, even at low tide. 



Between the two divisions of the reef, the elevated outer por- 

 tion and the fiat inner one, there is the most marked contrast. 

 While the latter has been completely smoothed and rounded off, 

 so that scarcely any angles remain upon it, the former retains all 

 the possible roughness that could be brought together on so nar- 

 row an area. The entire raised mass of rock is full of holes of 

 every imaginable size and shape, the margins of which are always 

 acutely angulated. Every little surface that is not pointed in 

 itself is surmounted by a large and strong barnacle with sharply- 

 edged valves, and large clusters of digitate projections stand up 

 at frequent intervals. This combination of surface is a very unin- 

 viting one to look upon, but it is far less pleasant to climb over 

 it or walk along its upper part. The outer slope is by far the 

 most irregular, as the waves, aided by an army of sea-urchins, 

 have broken into it and hollowed out thousands of ragged holes, 

 which, lying concealed beneath the seaweeds, might lead to many 

 accidents were the reef more frequented. 



The outer portion of the reef is of a dark and rather rich 

 brown color when wet by the waves, but nevertheless has quite a 

 dead appearance. Examining carefully this brown rock, it is seen 

 to consist generally of an accumulation of very small worm tubes, 

 closely packed together and forming a very hard mass. The sur- 

 face of the low inner level is of a much lighter color, a rather 

 faded brown, and looks even more lifeless than the part we have 

 been describing; no barnacles or other large animals grow 

 upon it. 



What forms of life occur about the reef? On the outer side, 

 reaching to a height of a foot or slightly more above ordinary 

 low tide, is a luxuriant growth of seaweeds. Over the same zone, 

 but not so apparent, spread encrusting nullipores, which, though 

 resembling lichens in form, are so highly charged with lime as to 



