1 879-] Pf'of. Hartt on the Brazilian Sandstone Reefs. 357 



every sand-beach in the world, we will hastily glance at the other 

 evidences of the same phenomena on the Brazilian coast. 



The northern-most consolidated beach examined by the Geo- 

 logical Commission, is near the mouth of the Rio Parahyba do 

 Norte, where, to the south of a fringing coral reef, there are traces 

 of a short and imperfect stone reef lying upon the shore. Stone 

 reefs have, however, been recorded from north of this point by 

 other observers, but they have never been described ; one is situ- 

 ted at the mouth of a small river, about eighteen miles north of 

 the Parahyba do Norte, and another lies in front of the Rio 

 Potengy, in the province of Rio Grande do Norte. 



Directly to the south of Cape Sto. Agostinho. in Pernambuco, 

 is the most perfect stone reef discovered; it is almost absolutely 

 straight, its northern end being separated from the cape by only 

 a narrow break or bar, encumbered by loose blocks of reef rock. 

 The land back of the reef, being very low, has been swept deeply 

 away, forming a broad and very shallow bay. The inner edge of 

 the reef is honeycombed and as irregular as that of a coral reef, 

 while the shallow basins of the median and inner portions of the 

 surface are much developed, forming regularly terraced plateaux. 



At Rio Formoso, in the same province, there is another stone 

 reef, reaching only about three feet above mean low tide, and not 

 having a great length. The joints dividing the reef-rock are often 

 filled in with sand, which has sometimes been solidified. On the 

 island of Santo Aleixo, not far distant from Rio Formoso, is a 

 small reef of soft texture, lying alongside the beach, and other 

 imperfect reefs also occur in this vicinity on the main shore. 



Nowhere near the city of Bahia do we find perfect sandstone 

 reefs; but at the mouth of the bay of Bahia, close to the light- 

 house on the outer shore, and on some of the inner shores of the 

 bay, layers of consolidated material occur, capping the beaches 

 and at times covering quite extended areas. They are often com- 

 posed of very coarse materials and contain many shells, and illus- 

 trate beautifully, in many cases, the irregularities of beach bedding. 



On the western side of the same bay, at Porto Santo, there is 

 a curious example of consolidated beach structure, the only 

 instance of the elevation of such material of which we are aware. 

 At this place we find a cliff back of the beach, having a length 

 of about 1,100 feet, and a greatest height of about thirteen feet, 

 and composed almost entirely of sand and gravel, cemented by 

 lime into a sandstone. The lower part of the cliff is very hard 



