136 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 and 
into the river’s channel an enormous delta 
of new material that considerably narrowed 
the channel 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 Lagóa de Sinimbá in 
the State of Parahyba do Norte. Suppose 
` а flood or any agency whatever should cause 
the waters from Lagóa Sinimbú to cut 
Ocean 
through the narrow sandy neck north of 
the village of Traição. It is evident that 
the waves would immediately, or as soon as 
this extraordinary agency ceased to Бе 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 Alagóas. 
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 years 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 ав rios 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 
Fie. 78. Breached sand neck, 
Мо Una. 
