BRANNER: the stone reefs of BRAZIL. 



253 



near the margins of tlie 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 



Fig. 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 



i-r 



Fig. 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. 



