1879.] Prof. 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 
