134 bulletin: museum of comparative zoology. 



metres wide, and is piled with dunes, some of them as much as ten 

 metres high, but at and north of the village the rim is only about 

 forty metres wide and two or three metres high. The land side of the 

 lake is of Tertiary (]) sediments rising in a plateau from twenty to 

 thirty metres high. A section from Sao Miguel church on these hills 

 across the lake is given herewith. 



Fig. 71. Section from the hills at S. Miguel church across Lagoa Sinimbil. 



The history of the place appears to be as follows : when the Tertiary 

 sediments that form the coast plain rose from beneath the sea, they 

 reached an elevation considerably higher than that at which they now 

 stand. Erosion followed, cutting narrow valleys in these beds ; then 

 came a depression that carried beneath the sea the lowlands near the 

 coast and the lower ends of some of the valleys. Marine erosion on the 

 newly exposed beach-lines tore down the headlands, and the sands were 

 heaped up by the waves as sand-bai's which, in time, separated the salt 

 from the fresh water. 



The lakes along the coast of Ceara are produced, in my opinion, in 

 one of two ways, either by the throwing up of beaches by wave action 

 like those on the sandy west coast of France,^ or else by the shifting 

 sands of the dunes damming back or changing the courses of rivers, as 

 is known in Eio Grande do Norte, Ceara, and in Sergipe.^ 



One of the chief reasons for believing that certain lakes have been 

 shut in by the constructive action of the present sea and not simply to 

 have found ready-made basins is that if an opening be made in the rim 

 separating the lake from the sea the breach is immediately closed by the 

 sea. The lower courses of many of the rivers stand in the same relations 

 to the sea as do lakes similarly located, except that the rivers are cer- 

 tainly more capable of keeping tlieir mouths open than are lakes. 



Rios tapados. — The city of Eecife stands upon a long tongue of land 

 behind and around which flow the Beberibe and Capibaribe rivers. 

 Among the various plans for improving the port of Pernambuco one 



1 Andre Delabecque. Les Lacs Franr-ais, p. 47-49. Paris, 1898. 



2 See J. C. Branner. Cretaceous and Tertiary geology of the Sergipe-Alagoas 

 basin of Brazil. Trans. Amer. Phil. Soc. 1889, XVI., p. 375. 



