20 Annals of the Carnegie Museum, 



Alagoas throw much light upon the geographic development, not only of 

 this state, but of a large part of northeastern Brazil. Reference is here 

 made to the lakes that are so characteristic of that state. 



The accompanying map (Plate II) shows how the lakes of the coast of 

 Alagoas are distributed It should be noted that the lakes are not parallel 

 with the coast, but that their longer axes are approximately at right 

 angles to the coast. These lakes are all separated from the sea by low 

 flats of loose sand, which are occasionally drawn out into long narrow 

 spits. In all cases the lakes are being gradually filled up by the silts 

 washed into them from the surrounding high grounds. 



These geographic features all seem to be satisfactorily explained on the 

 theor}' that the coast formerh' stood considerably higher than it does at 

 present. At the time of this elevation the shore line was somewhat 

 further east, and, owing to the greater height of the land, the rainfall 

 was probably somewhat greater than it is now. At that time the lakes 

 did not exist, but streams flowed across the coastal belt and cut in the 

 soft sediments many deep, steep-sided gorges. A long period of uplift 

 and erosion was followed by a depression which carried the bottoms of 

 the gorges well below the level of the ocean, so that the salt-water backed 

 up in them and made estuaries of them. The shore line was shifted 

 somewhat further inland, and the waves soon cut into the soft materials 

 of the head-lands, threw the shore sediments back into the mouths of the 

 estuaries, and eventually turned them into lakes. The sediments. washed 

 into the lakes from the sides and at their upper ends gradually filled them 



Fig. 13. The channel of the Rio San Francisco, looking up stream, seen from 

 the Sugar-loaf hill at Pao d'Assucar, state of Alagoas, 



