12 J. C. BRANNER — STONE REEFS ON COAST OF BRAZIL 



The writings 'of early travelers on this subject have at least this value, 

 they show that there have been no marked changes in the elevation or 

 appearance of the reefs during the last 250 years or more. Only four or 

 five persons have written short articles of value upon the geology of the 

 Pernambuco reef; these are Darwin, Hartt, Rathbun, and Hawkshaw, 

 and perhaps Liais. With the exception of the two reefs south of Bahia, 

 described by Hartt, little was known of the other stone reefs prior to 

 the personal examinations made by the present writer. 



The theories of the origin of the reefs put forward by these authors 

 are all more or less correct so far as they go, but none of them take into 

 consideration the fundamentally important factors in the case, namely, 

 (1) the age and submarine topography of the coastline; (2) the con- 

 centration of the rainfall and periodicity of the streams ; (3) the influence 

 of a tropical climate ; (4) the aridity of the interior ; (5) the density of 

 the sea water ; and none of them account satisfactorily for the straight- 

 ness, uniform width, or the shallowness of the lithifled portions of the 

 reefs or for their peculiar and restricted geographic distribution. 



Commercial Importance of the Reefs 



Inasmuch as the northeast coast of Brazil is without large bays, ex- 

 cepting that of Bahia, these stone reefs have pla}^ed an important part 

 in the commerce of northern Brazil. They form small harbors, behind 

 which the little cities have grown up, or where the coasting vessels load 

 and unload, or take refuge during stormy weather. The largest city 

 built behind a reef is Pernambuco, and that is a city of 190,000 inhab- 

 itants. The rock of the reef was formerly extensively quarried for build- 

 ing purposes. Nearly all of the old dwelling houses, stores, churches, 

 monasteries, fortifications, and occasionally the sidewalks of the cities 

 along the coast are made of stones taken from the reefs. Of late years, 

 however, the Brazilian government, realizing the danger of injury to the 

 ports, has wisely prohibited the quarrying of the reef rocks. 



Antiquity of the arid Climate 



Since Cretaceous times there have been important geographical changes 

 in the Amazon Valley region, but about the northeast corner of Brazil 

 there have been no such changes. It is highly probable, therefore, that 

 the fatal drouths common in Ceara and the adjoining states of Brazil 

 have been characteristic of that region since Cretaceous times, and they 

 must continue to occur as long as the present geographic conditions re- 

 main. It follows also that reefs like the existing stone reefs have char- 

 acterized this coast certainly as far back in the history of the continent 

 as Eocene times and probably somewhat earlier. 



