768 THE JOURNAL OF GEOLOGY. 



explanation of this water-worn material seems to be that the Tertiary period 

 was closed by a depression along the present coast, which carried the beach 

 line far inland, or that it was already there. Then followed a gradual 

 emergence, 1 during which the whole area now covered by this widely dis- 

 tributed water-worn material was passed gradually 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 pebbles 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 pro- 

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

 in the course of the land's emergence, the soft, sandy and clayey beds of the 

 Tertiary were brought up 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 Tertiary beds they were deeply eroded, and the mud which originally made 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 the 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." 



GLACIAL TOPOGRAPHY. 



Agassiz considered that the undulating outlines of the topo- 

 graphy about Rio de Janeiro were attributable to glacial action, 2 

 though he recognizes the fact that nothing of glaciation was to 

 be learned from their appearance. 3 A careful study of those 

 features, made with this suggestion in mind, shows that the 

 rounded hillsides have no uniformity in their arrangement, that 

 is, what would be stoss sides, judging from the topographic forms, 

 face now in one direction, and now in another, and that the out- 

 lines are simply those produced by ordinary decomposition and 

 erosion, though much influenced by structural features. Hartt's 

 opinion, as originally expressed in his book (p. 33), was that the 

 forms of the hills were "due primarily to subaerial denudation." 



THE ABSENCE OF STRLE. 



A bit of negative evidence of great importance against the 

 glacial hypothesis is the fact that nowhere has there been found 



1 See also Pissis in Comptes Rendus de 1' Acad, des Sci., 1842, XIV., 1046. 

 2 Geological Sketches, II., 157. Bui. de la Soc. Geol. de France, 1867-8, XXV., 687. 

 3 Journey, pp. 69-70. 



