BKAXNER: THE STONE EEEFS OF BKAZIL. 73 



south of the Rio Tatuoca is a small isolated Tertiary hill, and the hydro- 

 graphic chart shows another of similar form a little further south. 



The essentia] features of the geology of the region consist of a ridge of 

 granite and granite porphyries, and other crystalline and metamorphic 

 rocks of the Cape having an east-west trend, and with Tertiary sediments 

 deposited against and over them. Denudation has stripped olf most of 

 the beds that lay upon the Cape crystalline rocks, and has carved out the 

 embayment that now opens south of it. The shore of the bay from 

 the Barra do Suape to the village of the same name is all of crystalline 

 rocks ; a little west of the village a promontory of Tertiary (?) beds 

 projects into the valley. This hill is of mottled yellow, red, and Avhite 

 clays and sands; there are no granites exposed where the Rio Suape 

 washes its base. 



At the village of Suape the beach on the flat is all sandy, and barely 

 high enough to keep the salt water at high tides from flowing over into 

 the fresh- water marsh lying just west of it. Tradition says that the bay 

 at this northern end is rapidly cutting away its western shore. The coco 

 palm stumps standing in the bay from one hundred and fifty to two hun- 

 dred metres out from the present beach bear out this tradition. 



At low tide great sandy flats are uncovered in the bay. At its south- 

 ern end and south of Camboa Point the bay is but a narrow and shallow 

 pool some twenty to fifty metres wide, into which the tide-water backs. 

 On the sea side of this pool is the wall-like reef, and on the land side a 

 bank of white sand five or six metres in height. The sand flats about 

 the mouth of the Ipojuca and in this arm of the bay swarm with myriads 

 of little fiddler crabs. These sands also contain a great number of deli- 

 cate pink sliells of bivalves. 



The sand ridge on the land side is a wind accumulation ; behind it the 

 country drops off" again to a somewhat lower level. 



The Cabo Santo Agostinho reef properly speaking begins on the beach 

 of the cape itself, just north of the Barra do Suape and a few hundred 

 metres north of the old fort. The rocks of the cape just here are coarse- 

 grained granites, and the reef rock lies unconformably against, and 

 attached to, these granites. There are several of these reef fragments 

 separated from one another by breaks of various lengths and strewn along 

 the beach over a distance of a kilometre to the north of the fort. The 

 section is essentially the same for all these remnants. 



Tlie fragment nearest the fort is fifty-three metres wide by forty-five 

 metres long. The next fragment to the north is ninety metres long 

 and about fifty metres wide. All these reef remnants have a gentle sea- 



