262 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



those of Ci*etaceous age. In the rocks known to be of Tertiary age there 

 is i)ut little evidence of the existence of coral reefs. The geographic de- 

 velopment of the coast, however, and the distribution of the reefs at the 

 present time lead to the inference that the reefs, as they are now known, 

 began their existence after the elevation and erosion of the Eocene Ter- 

 tiary beds along the Brazilian coast. This is suggested, if it is not 

 pi'oved, by the fact that the present reefs grow upon the marine shelf 

 cut by the sea in the Tertiary and older rocks, or they occupy areas that 

 were submerged after the erosion of the Eocene beds had been in process 

 for a considerable period. There has been much encroachment upon the 

 land by the sea, and this encroachment has been followed up sharply by 

 corals taking possession of the submarine shelves wherever the conditions 

 were favorable until we now have coral reefs growing close to the sea 

 bluffs. The reefs at and about the Abrolhos group are built upon sub- 

 merged Tertiary rocks. They therefore began in the latter part of the 

 Tertiary and have continued down to the present time. This seems to 

 be true of all the large reefs : those of the Abrolhos, Parcel das Paredes, 

 and those at Cape Sao Roque ; and these reefs are not only the largest, 

 but likewise the oldest and probably the thickest of the reefs of the 

 Brazilian coast. Many of these reefs, however, long ago finished their 

 upward growth and are now growing only laterally. 



For reasons already given the barrier and fringing reefs that grow 

 near the steep shores appear to be newer than the large offshore reefs. 

 ]Sro line of demarcation, however, can be drawn between the large off- 

 shore reefs and the near-shore barrier and fringing reefs. They all 

 merge together both in physical characters, in thickness, and in age. 



The coral reefs, therefore, antedate the stone reefs. This is shown by 

 the occurrence of reef-building corals in the rocks of the stone reefs, and 

 also by the relative positions of the two kinds of reefs, along the coasts. 

 The coral reefs are also locally newer than the stone reefs, as is shown by 

 the former growing upon the latter. The corals will continue to grow 

 seaward from the stone reefs, while the latter will change but little. No 

 elevated coral reefs are now known on the coast of Brazil. If the eleva- 

 tions of Pliocene times 'killed some of the reefs, they were again taken 

 possession of and new reefs grew upon the old ones as soon as they were 

 resubmerged. 



The Brazilian coral reefs are almost everywhere narrow. The wid- 

 est are those of the Abrolhos, Parcel das Paredes, Itassepanema, Ita- 

 columis and Cape St. Roque, which are at most only about thirty-three 

 kilometres wide. Some of the coral reefs connect with the land and 



