Branner : Gkologv ok Alagoas, Brazii,. 



21 



up so that some of tluMii lia\o already boon turnod iiite) marshes, and the 

 same process will, in the course of time, obliterate all of them. Lagoa do 

 Norte may be taken as a type of the larger ones of these lakes. This 

 lake has now silted up to such an extent that it is navigable only for vessels 

 drawing a little more than one motor, and that too along a single channel 

 on the south side of the lake. 



At the time when the region stood higher the lower Rio S. Francisco 

 ran through a steep-sided gorge, and the streams entering it from the sides 

 cut their channels down to or nearly to the level of the main stream. 

 When the depression came the lateral streams were flooded and their 

 former channels are now marked 1)>' lakes, marshes, or broad flat river- 

 bottoms. 



While the coastal lakes have been filling u\^ with silts from inland, those 

 washed from the immediate coast have accumulated locally under the 



Fig. 14. Section showing the relation of the deep well at Maceio to the rocks 

 of the hills above the city. 



protection afforded by the coral reefs which thri\e along some parts of 

 the coast of Alagoas. In such places the land has been gaining on the sea. 

 Jaragua, the southern part of the city of Maceio, for example, is built 

 upon low ground that lies between the city proper and the coral reefs 

 which help to form the harbor of Maceio. A well two hundred meters 

 deep put down several years ago at the railway shops in Maceio was 

 entirely in loose materials. This fact leads one to conclude that the steep 

 slope of the blufTs, on which the light-house stands, extends for at least 

 two hundred meters beneath the surface of the ground, for these loose 

 materials are not the plateau beds in place, but the later deposits laid 

 down since the depression of this region. 



Stone Reef. — About three kilometers north-east of the Barra de Sao 

 Miguel on the Alagoas coast is a beautiful example of a stone reef. The 

 accompanying panorama (Plate III) made by my assistant, Mr. Roderic 



