368 G. A. Waring — Reef Formations of. the 



periods of storm, and are hence of uncertain flow ; for as is 

 true in other arid regions, the rainfall of northeastern Brazil 

 is very irregular in amount and distribution. 



Calcareous Sandstone. 

 Reefs. General features. 



At certain places along this coast there are sandstone reefs 

 whose character and appearance is considered by scientists and 

 others who have seen them to be almost unique. The only 

 other known occurrences of a similar formation appear to be 

 at a few places along the eastern shore of the Mediterranean 

 and on the borders of the Red Sea, and little information is 

 available concerning the reefs of these localities. The best 

 known reef on the Brazilian coast is that which protects and 

 in fact forms the harbor of Pernambuco, in about 8 degrees 

 south latitude. This reef has been described or mentioned by 

 numerous writers. In 1S36 Charles Darwin in writing of it 

 said that " at first sight it is difficult to credit that it is the 

 work of nature and not of art.' 1 * 



Dr. J. C. Branner, President of Stanford University and 

 head of its geological department, who has worked on the 

 geology of Brazil for many years, has published an exhaustive 

 study of the reefs.f The principal features of the reef have 

 also been summarized by him in a later paper,:}: and may be 

 stated as follows : 



The reefs are long, narrow, and nearly straight, and are situ- 

 ated in most instances near the mouths of streams and nearly 

 parallel to the present beach. At some places where reefs 

 have been formed, the reef is not connected with the land ; in 

 other places one end is exposed on the beach or is buried 

 beneath the sands, while in still others the reef lies as a whole 

 along the present beach. The axis of each reef is practically 

 horizontal and lies at about high-tide level. Its top, however, 

 slopes gently seaward and in section the material also exhibits 

 bedding planes that dip at low angles toward the sea. While 

 the better-developed reefs are as a rule nearly continuous, in 

 many places they are cracked, broken and undermined by the 

 surf, and many of the smaller reefs have been greatly broken 

 up by this means. The lithified material is only ten or fifteen 



* Journal of Researches into the Geology and Natural History of the vari- 

 ous countries visited by H. M. S. Beagle . . . from 1832 to 1836. London, 

 1839, p. 593. 



f The Stone Eeefs of Brazil, their geologic and geographic relations, with 

 a chapter on the coral reefs, Bull. Mus. Comp. Zoology, vol. xliv, Geol. 

 Series vii, Cambridge, 1904. 



X Stone Reefs on the Northeast Coast of Brazil, Bull. Geol. Soc. Am., vol. 

 xvi, pp. 1-12, Feb., 1905. 



