468 B. Rathhun — Geology of the Lower Amazonas. 



Mr. Derby refers the sandstone hills of the Erere series, 

 which surround the Devonian plain of the same name, to the 

 Cretaceous, from a study of the leaves of dicotyledonous plants, 

 contained in some of the beds. These hills, which are com- 

 posed of inclined strata, were elevated during, or at the close 

 of, the Cretaceous age, as a broad anticlinal ridge, afterwards 

 denuded away in the central portion, so as to uncover the De- 

 vonian plain, and leave the present series of monoclinal ridges, 

 disposed in the shape of an ellipse. 



Much of Mr. Derby's paper is also devoted to the extensive 

 Tertiary deposits and the varzea of the Amazonian valley, sub- 

 jects already treated of at some length by Prol Hartt. 



