198 bulletin: museum of comparative zoology. 



The stratigraphic relations of the reefs to the Tertiary beds are 

 matters of conjecture rather than observation. There are, to begin 

 with, but few places along the coast where both Pliocene beds and 

 sandstone reefs occur side by side. One of these is at Rio Formoso, 

 Estado de Pernambuco, where the stone reef is one and a half kilometres 

 from the Pliocene exposures on the Praia da Gamella. 



At Seriuhaeni the Tertiary is exposed on the side of the river at the 

 town, and the reef does not touch them. 



At Mamanguape the relations of the Tertiary sandstones and the 

 reefs appear to be as shown in Figure 8, page 29. 



At Rio Formoso and Seriuhaem the Tertiary is considerably higher 

 than the sandstone reef; at the Mamanguape locality, there seems to 

 be but little or no difference of level. 



On the shore of the mainland opposite Catu on Itaparica Island, 

 Bahia, there is a long low sandstone bank that I take to be Pliocene. 

 Thei'e are no stone reefs near this, however. 



At other places the relations of the stone reefs to rocks of known age 

 are not shown, but there are no facts in my possession that are not in 

 accord with the theory that the stone reefs are newer than any other 

 consolidated sedimentary beds along the Brazilian coast. 



Physiographic relations. — The relation of the reefs to the adjacent 

 shores is accepted as evidence of the recent date of some of the reefs, 

 while the process of their formation strongly suggests, if it does not 

 prove, that the low, flat lands behind the stone reefs are underlain by 

 other stone reefs. Seashores are rarely at a standstill ; they are either 

 being cut away or built out. Their elevation, as compared with that of 

 the land and their marginal position relative to the flat country behind 

 them, show that the reefs and the flat lands are genetically related, and 

 that they are of about the same age. These flat lands are partly recent 

 deposits ; but they also extend back into the Pliocene. Their origin 

 is discussed in Chapter V. One of the most striking features of the 

 external stone reefs is their proximity to and parallelism with the shores 

 behind them. If a stone reef had been in existence for a long time, 

 speaking geologically, it would have been either obliterated by the 

 encroaching sea, or it would have been buried under the encroaching 

 land. 



The fossils in the reefs. — The fossils foiuid in the reef rock, so far as 

 they are now known, are the remains of animals now living in the seas 

 along side of the reefs. At Pernambuco, Rio Formoso, and Mamanguape 

 the most common fossils are the shells of " mariscos " (a species of 



