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BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



the rainy season the river had sapped the sand-bank that separated it 

 from the sea, but the next incoming tide had thrown the sand back into 



the opening, and had heaped into it aud 

 into the river's channel an enormous delta 

 of new material that considerably narrowed 

 the i-hannel and that the river must now re- 

 move. At the next high tide the sea would 

 be able to more than complete the repairs of 

 the breach. 



The same phenomena were observed five 

 hundred metres above the mouth of Rio da 

 Cruz, the small stream next south of Abreu 

 de Una. The breach on the Rio da Cruz 

 was only about sixty metres wide. 



With these illustrations in mind let us 

 turn to the case of Lagoa de Sinimbu in 

 the State of Parahyba do Norte. Suppose 

 a flood or any agency whatever should cause 

 the waters from Lagoa Sinimbu to cut 

 through the narrow sandy neck north of 

 the village of Traiqao. It is evident that 

 the waves would immediately, or as soon as 

 this extraordinary agency ceased to be ac- 

 tive, throw the beach sands into the breach and turn the drainage 

 away to the south where it can join its forces to those of the Maman- 

 guape River and get into the sea under the cover of the mangrove 

 swamps, sand-bars, and stone reefs that there protect it from the 

 ocean. 



One of the most impressive examples of the damming in of the coast 

 lakes by the sea is that of the Rio Jacaresica a few kilometres north of 

 the city of Maceio, State of Alagoas. 



That stream is shown upon the hydrographic chart as flowing into 

 the sea, and doubtless at one time it did so, but when I passed along 

 that beach in August, 1899, no such stream was flowing across it, and I 

 was informed by residents that for fifteen or twenty j^ears the Jacaresica 

 had been a rio tapado, or stream with its mouth closed. 



In this connection I am reminded that there are several small streams 

 along the Brazilian coast known as /-/ox tapados. One of these is only a 

 few kilometres north of Olinda on the Pernambuco coast. 



The following sketch was made on the coast between Rio da Cruz and 



Fig. 73. Breached sand neck, 

 Rio Una. 



