woodworth: geological expedition to brazil axd chile. 101 



which also surround former rocky islets and unite them to the 

 mainland. 



Off the coast from the entrance of Rio Harbor southwestward 

 to and beyond Laguna, low rocky islets of granite or gneiss reveal the 

 continuation of the dissected slope of the Serra beneath the sea. 

 These islands are of small size and mostly uninhabited except by 

 occasional fishermen or as they may be the site of a lighthouse. Navi- 

 gation between them is dangerous because of the fogs at certain 

 seasons of the year and for the reason that lesser islets, or rocks which 

 just reach the surface of the sea, are not wanting. 



These off-shore islands are frequently partly surrounded by a plat- 

 form of rock rising a few feet above sea-level. These benches corre- 

 spond to the elevated strips about the bays and probably indicate the 

 extent to which the subaerial upper portion of the island was reduced 

 by weathering and the attack of the sea above the level of these 

 platforms during the episode of maximum depression. 



Bordering the inner shore of the bay of Paranagua, there are rem- 

 nants of siliceous sands of presumably Tertiary date which appear to 

 have been deposited within the dissected slope of the Serra do Mar, 

 showing that the basal portion of the coastal slope was well dissected 

 before the close of the Tertiary periods. 



Professor Hartt found evidence at various points along the coast 

 that an elevation or negative delevelling had recently taken place. 

 ^Yhether the coast from Rio de Janeiro southward is now under- 

 going a slow delevelling or not I could not ascertain. Faint traces 

 of an old beach not now reached at high tide near Paranagua favors 

 the idea of a recent elevation there. 



The hypothesis above advanced of the warping up of the south 

 Brazilian plateau with the axis of curvature along the Serra do Mar 

 belt and the reference of the now dissected surface of a former pene- 

 plain to a Cretaceous date is based upon the fact that in the region of 

 Bahia the Cretaceous strata extend far inland. It is thought that 

 similar conditions prevailed on the south during a stage in the evolu- 

 tion of the present topography, that with the negative delevelling and 

 the development of a steep slope to the sea and a gentle slope towards 

 the interior the Cretaceous strata were denuded in early Tertiary 

 time. The Tertiary basin in the valley of the Parahyba between the 

 Serra do Mar and the Serra da Mantiqueira is taken as evidence of 

 uplift and dissection of the Cretaceous peneplain prior to the deposi- 

 tion of the Tertiary fresh-water beds. The definite determination 

 of the date of the Tertiary deposits would fix the limits of time to be 



