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BRANNER: THE STONE REEFS Of BRAZIL. 253 
near the margins of the reefs. These living corals are fully a metre 
below the reef’s flat surface. 
The surface of the reef — that is, of the large solid portions that rise 
above water — usually slope off rather gently into the water at all points 
where it was examined. The slope of from three to ten degrees begins 
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Fie. 101. Profile of the edge of Lixa coral reef, 
from fifty to one hundred metres back from the edge of the water at 
low tide. 
At several places this gentle surface slope continues beneath the water 
for a hundred, or even several hundred, metres, where it comes to a 
sudden drop off into deep water. 
The patches of living corals that rise from the deeper waters in the 
channels and at the reef margins are of many sizes. Their forms vary, 
of course, but not to any remarkable extent. The following are true 
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Fra. 102. Vertical sections showing the forms of growing coral masses on 
the Lixa reef. The broken line represents low tide. 
profiles as nearly as they can be made without minute measurements, 
and they include as great a variety of forms as was seen. 
