46 BULLETIX: MUSEUM OF COMPAKATIVE ZOOLOGY. 



sand which everywhere has the appearance of having been blown up 

 from^the beach. In places this sand ridge is scarcely high enough to 

 keep the spring tides from flowing over it into the lake, but at one place 

 south of the village it has a height of nine metres on the seaward side. 

 From the village northward to the base of the hill on which the old fort 

 stands this ridge is only from sixty to one hundred and twenty metres 

 vf'ide from fresh water to highest tide-level on the sea side. South of the 

 village it widens out somewhat, and at one place is two hundred metres 

 wide. The drainage of the lake is thus compelled to seek an outlet 

 through the Rio Mamanguape, ten kilometres south of the low narrow 

 neck north of Traigao. 



Plate 30 shows this neck of sand with the bay to the right and the 

 marsh of Lagoa de Sinimbu on the left. 



A line of levels run across this neck shows that the lake water on July 

 24, 1899, was fifty-nine centimetres lower than the level pointed out as 

 that of the highest spring tides on the sea beach. The mean tide- 

 level, however, is a metre or more lower than the lake surface. 



The Lagoa de Sinimbu and the flat lands about it and about the 

 mouth of the Mamanguape lie as one broad flat region behind the reefs 

 of Traigao and Mamanguape alike. For a fuller discussion of these 

 geographic featui'es and their history and bearing upon the reefs the 

 reader is referred to Chapter V., pp. Ill to 170. 



The Traigao end of the reef ends rather abruptly, standing boldly out 

 to sea. At low tide one can walk dry-shod from Traicao Point out on the 

 stone reef, so that it may be said to join the land at that place. South of 

 Traigao Point the land draws away from the reef, forming thus the north- 

 em part of Mamanguape Bay, while north of the point the land swings 

 away still more sharply to form the Bahia de Traicao. A good view of 

 the bay is had from the site of the old abandoned fort north of the town ; 

 fi'om this point the photographs for Plates 29 a and 29 b were taken. 



The Trai^'ao reef has a total length of only a little more than two 

 kilometres ; this does not include the fragments or outliers that connect 

 this with the Mamanguape reef. Those fragments alone down to the 

 bar have a total length of 2.4 kilometres. 



A glance at the map shows that Traicjao reef has a gentle outward 

 curve at Traigao Point. It is rather broken, and its outer edge is 

 ragged. In several places the waves are undermining it from the out- 

 side. On the whole it is a flat and rather smooth reef. Along the 

 inner margin are the usual points left by surface etching, but they are 

 not so high or so prominent a feature of this as of the Mamanguape 



