3SS G. A. Waring — Reef Formations of the 



whether or not the iron-cemented rock exists at this place. 

 Two wells that were drilled to depths of more than 50 feet at 

 Camocim, 2 or 3 miles from the ocean and several hundred 

 yards from the harbor, did not encounter iron-cemented 

 material. 



Although the evidence here advanced is slight, it is believed 

 by the writer that the iron-cemented material which forms 

 most of the fringe reefs and probably some of the off-shore 

 reefs as well, is not a definite bed in the Tertiary coastal sedi- 

 ments, but is a hardened phase in them produced by the 

 concentration of the iron ; and that this concentration and 

 hardening is limited to approximately sea level and extends 

 only a short distance back from the shore. 



Coral Reefs. 



In addition to living coral reefs which exist off-shore between 

 Rio Grande do Norte and Macau, a few reefs that now join 

 the land have their upper portions, at least, composed of dead 

 coral material. These reefs are here noted chiefly to extend 

 northward the records of Dr. Branner on the presence of such 

 reefs and the evidence that they furnish of a comparatively 

 recent slight elevation of the coast. The corals can have 

 grown only when they were under the ocean water most of the 

 time, and the presence at some places of their remains entirely 

 out of water shows that the coast at those places has been 

 uplifted a sufficient amount to bring the corals into their 

 present position relative to sea level. 



An organic formation that is not coral but which seems 

 worthy of mention is a soft stone formed by worms that 

 cement together grains of beach sand. This material was 

 observed at only two places : on blocks of iron sandstone on 

 the beach at Ponta Morcego, and to lesser extent on rocks at 

 Ponta Genipabii a few miles northward. Dr. Branner men- 

 tions having observed the material farther south, it being 

 especially well developed near Bahia Formosa, 45 miles south 

 of Ponta Morcego. 



The outer portion of the fringe reef at Ponta Genipabii is 

 overlain by flat-topped masses that are covered to a thickness 

 of several inches with brown, calcareous tubes and the remains 

 of other forms of sea life. It is the only reef where such 

 material was seen. The main part of the reef is, however, of 

 the common iron-cemented sandstone. 



About three miles westward from the village of Cajueira a 

 bluff which rises at the upper edge of the beach to a height of 

 8 or 10 feet exposes for several yards a cream-colored to rust- 

 colored rock that apparently consists of quartz grains cemented 



