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bulletin: museum of comparative zoology. 



back into the estuaries and gradually formed bars across their' mouths, 

 choking up their outlets, and thus turned them into brackish water 

 bodies. Their end it is easy to foretell : they will gradually become 

 smaller and shallower, and at no distant day will be great marshes, each 

 with a sluggish stream winding through it, and still later low flat vat^zeas. 



Fig. 69. 



On the coast between Rio de Janeiro and Cape Frio are several lakes 

 shut in by the coast sands that have been thrown across the mouths of 

 valleys opening toward the sea. The country immediately north of these 

 lakes is a mountainous one, the land rising to elevations of from one 

 thousand to fifteen hundred metres in a distance of thirty or forty kilo- 

 metres. Between some of the lakes low headlands come down to the 

 beacli. Lagoa Marica, for example, has such headlands at both its 



