78 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



but it shows very little or no signs of active or rapid wearing of the 

 rocks. 



The surf that breaks against the outer face of the reef is heavy, for it 

 comes in from an open and deep ocean where there are no coral reefs to 

 break its full force. The depth of 4i fathoms marked on the hydro- 

 graphic charts outside comes close up to the reef along most of its 

 length. It is remarkable that this violent surf has not affected the reef 

 more than it has. There are but few blocks tossed upon the top of it ; 

 one of these, however, weighing more than forty-eight short tons, has 

 been hurled almost the entire width of the reef, and now^ rests within a 

 few metres of its inner margin. 



Mention should here be made of the possible relations of the Cape 

 Santo Agostinho reef to a small coral reef just off Cupe Point. The 

 stone reef is in line with the beach to the south for half a kilometre ; the 

 beach then swings eastward to and around Cupe Point. East of this 

 point a coral reef about six hundred metres long lies a few hundred 

 metres off shore. Now the Cape Santo Agostinho reef, like the others, 

 has a gentle seaward dip. If this reef continues southward to and 

 passes beneath the sands west of Cupe, its dip must carry it beneath 

 the coral reef that lies east of that point. (See map of Cape Santo 

 Agostinho reef, p. 71.) 



The beach rocks at Porto de GaUinhas. — Porto de Gallinhas is a little 

 village on the coast fifteen kilometres soiith of Cape Santo Agostinho. 

 It is on a sandy flat with fresh-water marshes between the village and 

 the hills just west of it. 



There are some rocks of recent origin at this place which, on account 

 of their possible relations to the coral reef off the coast, are worthy of 

 mention. These rocks are like the ordinary reef rocks, except that 



Fig. 48. Section showing the relation of coral reef to beach sandstone at 

 Porto de Gallinhas. 



they contain rather more than the usual amount of calcareous Algae 

 fragments. They are exposed when the tide is out at the large ware- 

 house that stands on the edge of the beach near the anchorage. Again, 

 south of the village, at the first westward turn of the beach, soft cal- 

 careous sandstones are exposed on shore by the recent encroachment 

 of the sea. These beds have the usual seaward dip, which, if it con- 



