254 



J. C. Br (inner — ^Eolian Sandstones of 



Ilha Raza, Sella a Gineta, Ilha do Meio, Ilha Rapta, and the 

 northeast point of the main island, while rain, charged with 

 carbonic acid, falling upon it, and the spray blown over it from 

 the surf, dissolved out the carbonate of lime, carried it down- 

 ward and re-deposited it, thus solidifying the sand into a hard 

 rock, upon which the ocean has gradually encroached from 

 both sides. 



1. 



, taL"'J:S*' -> - : - •#•-■?• ^^'- ^e„ 



Sandstone rim at the base of Atalaia Grande. 



The southeastern side of the island is being cut away much 

 more rapidly than the northwestern side. This is due to the 

 prevalence of east winds, and the northeast-southwest position 

 of the longer axis of the group.* On the south side the spray 

 attacks the rocks over the surface, while the more violent surf 

 undermines them. The action of both these forces may. be 

 seen in iig. 6. 



At the base of Atalaia Grande on its eastern side, the aeolian 

 sandstones form a narrow rim or shoulder, about one hundred 



* During the months of July and August, 1876, the wind was almost constantly- 

 from the east, varying occasionally to a few points south of east or north of east. 



