422 THE CERTACEOUS ANB TERTIARY GEOLOGY 



ally through the condition of a beach upon which the then loose, angular, surface 

 rocks of the country were rounded and worn into the boulders, cobbles and peb- 

 bles which we now find scattered over this region. While the surf was beating upon 

 and wearing the hard crystalline and metamorphic rocks of the interior it was unable 

 to produce any very marked effect upon the topography of the country, but when, 

 in the course of the land's emei-gence, the soft, sandy and clayey beds of the 

 tertiary were brought within its reach, the work of land sculpture it was able to do 

 was enormously increased. During the emergence of these tertiary beds they were 

 deeply eroded, and the mud which originally made part of them was washed seaward, 

 and their coarser materials were concentrated upon the slowly receding beach. In some 

 places these accumulations assume unusual proportions, as if they had been brought 

 together by the gradual beating of waves along a beach, or had been reconcentrated 

 by later streams. An example of this kind, outside the Sergipe-Alagoas basin, occurs 

 at the Camassari diamond washings in the province of Bahia (v. Plate V). It would 

 seem that during this period some of the wider valleys excavated in the tertiary were 

 formed. The concentration of coarse material left sjiread over the surface of the 

 remaining portions of the tertiary, and indeed over the whole country rising from the 

 bottom of the ocean, the thin covering of cobblestones, and pebbles such as we now 

 have. Later, by the oxidation of the iron in these beds they have been changed here 

 and there to a ferruginous conglomerate. 



The post-tertiary deposit is veiy widespread in Brazil, and has been referred by 

 both Agassiz and Hartt to glacial action. 



