134 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
metres wide, and is piled with dunes, some of them as much ав 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 (1) 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. 
lw. ; =. © я 
Fie. 71. Section from the hills at 5. Miguel church across Lagóa Sinimbú. 
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 ав sand-bars which, in time, separated the salt 
from the fresh water, 
The lakes along the coast of Ceará 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 Rio 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 their mouths open than are lakes. 
tios tapados. — The city of Recife 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 André Delabecque. Les Lacs Frangais, p. 47-49. Paris, 1898. 
2 See J. С. Branner. Cretaceous and Tertiary geology of the Sergipe-Alagóas 
basin of Brazil. Trans. Amer, Phil. Soc. 1889, XVL, p. 875. 
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