branner: the stone reefs oe brazil. 81 



the southeast corner rises to a height of twenty-one metres. On the 

 western side of the island is a small bay, south of which is a quarry 

 in the igneous rocks. Next to the quarry there are remnants of a 

 calcareous fringing reef upon the beach, extending from that point to 

 the southeastern point of the island. Along the shore of the little bay 

 on the south side of the island is a piece of consolidated beach or stone 

 reef. The rock is made of bits of shells, corals, sands, etc., exactly like 

 the unconsolidated sands of the present beach. It is not hard and solid 

 like the reef rock of Rio Formoso, but is soft and porous. 



This reef is between one hundred and fifty and two hundred metres 

 in length, is from four to five metres wide at the widest, and is so high 

 in places that only the very highest tides wet it entirely. On the land 

 side it is buried beneath the beach sands, but toward the sea it is abrupt 

 in places. It seems to be wearing away rapidly. 



The sandsto7ie reef of Rio Formoso} — Rio Formoso is an estuary in 

 the State of Pernambuco, sixty kilometres southwest of the city of 

 Pernambuco, and thirty-four kilometres southwest of Cabo Santo Agos- 

 tinho. An isolated Tertiary hill stands back from the coast west of 

 Gamella, and another stands just north of Rio Formoso. Against these 

 hills lies a plain of later geologic age, that rises about eight or nine 

 metres at most above high tide-level. Northwest of these hills, and 

 north of the estuary, is a broad, low, flat country partly covered by loose 

 sand and growing orchards of caju trees and other caatiuga plants, and 

 partly also by extensive mangrove swamps. Beyond (west of ) this flat 

 valley rise the low, approximately flat-topped table-lands of the interior, 

 — in this vicinity composed of granites, gneisses, and crystalline schists. 



The structure and character of the Tertiary hills is shown where the 

 tides of Rio Formoso have cut away the foot of the hill upon which 

 stands the Church of Nossa Senhora da Guadalupe. The rocks are soft, 

 white and gray sandstones, and red and yellow mottled clays dipping 

 gently seaward. 



The rocks that lie against these Tertiary hills are well exposed all 



nesian porphyries (p. 260). My determination of tliis rock was made after a 

 microscopic examination by the late Dr. George H. William from material gathered 

 by myself. 



(The Cretaceous and Tertiary geology of the Sergipe-Alagoas basin of Brazil. 

 By J. C. Branner. Trans. Amer. Phil. Soc, 18S9, XVI., p. 404, foot-note.) 



In his Climats Ge'ulogie, etc., da Bie'sV (p. 252), M. Liais speaks of Tertiary 

 sediments on the island. The beds he refers to are these recent sandstones. 



1 This description of the Rio Formoso reef has been published in Portuguese 

 by the Instituto Archeologico e GeographicoPernambncano at Pernambuco, Brazil. 



VOL. XLIV. 



