bkanner: the stone reefs of brazil. 49 



barely large enough for jangadas to pass through. The breaks are 

 most abundant south of Mamanguape Point where the outflowing river 

 strikes it. Several of the minor breaks, even at the lowest tides, have 

 the water flowing through them between and beneath the loose blocks 

 that fill them. 



Strictly speaking, the reef as a whole is not straight, but neither is it 

 very crooked. The bends in it are quite apparent when one sees the 

 reef itself, but on a map of small scale they hardly appear. These 

 curves are such as one may see on any approximately straight beach. 



Considered in cross-section, the surface as seen from the bar has a 

 gentle slope seaward. In most places the landward face is abrupt, and 

 the channel of the Mamanguape River passes close up against the reef- 

 wall. Toward the southern end, however, and especially where the 

 inner face has been protected by the secondary reef, the profile comes 

 down at a gentler angle or by a series of small steps or low terraces. 



Fig. 20. Section across the Mamanguape stone reef. 



The outer edge of the reef is here and there broken off" with beauti- 

 fully smooth vertical faces. But even in such cases it is protected to a 

 great extent by its own fragments, many or most of which are gigantic 

 blocks undermined on the seaward side and let down to where they now 

 lie. To a notable extent these blocks lie at angles that make them most 

 effective protective agents for the rest of the reef, and least liable to in- 

 jury themselves from the onslaught of the sea. The following examples 

 (Fig. 21) are types of the fractures observed on these faces. 



In all these cases the sea is to the right and the reef to the left. It 

 is noticeable in these instances that the broken fragments have the 

 appearance of having been let down by undermining, and they now lie 

 so as to serve as eff"ective protection to the remainder of the reef, 

 whether from undermining or surface wear. Many cases wei'e observed, 

 however, in which the fragments lie altogether at haphazard. 



Some sheer faces more than tln-ee metres high are openly exposed to 

 a tremendous surf apparently without being in the least afl'ected by it. 

 At one place there is such a face sixty-five metres in lengtli. Xow and 

 then one may observe, when the surf is powerful, that the shock or jar 

 of the blows is very marked over a given area. I take it tliat these 



VOL. xuv. 4 



