430 



A JOURNEY IN BRAZIL. 



waters. It would gradually deposit them in the valley 

 bottom in horizontal beds more or less regular, or here 

 and there, wherever eddies gave rise to more rapid and 

 irregular currents, characterized by torrential stratification. 

 Thus has been consolidated in the course of ages the 

 continuous sand formation spreading over the whole Ama- 

 zonian basin, and attaining a thickness of eight hundred 

 feet. 



While these accumulations were taking place within 

 this basin, it must not be forgotten that the sea was beat- 

 ing against its outer wall, — against that gigantic moraine 

 which I suppose to have closed it at its eastern end. 

 It would seem that, either from this cause, or perhaps in 

 consequence of some turbulent action from within, a 

 break was made in this defence, and the waters rushed 

 violently out. It is very possible that the waters, gradu- 

 ally swollen at the close of this period by the further 

 melting of the ice, by the additions poured in from lateral 

 tributaries, by the rains, and also by the filling of the basin 

 with loose materials, would overflow, and thus contribute 

 to destroy the moraine. However this may be, it follows 

 from my premises that, in the end, these waters obtained 

 a sudden release, and poured seaward with a violence 

 which cut and denuded the deposits already formed, wear- 

 ing them down to a much lower level, and leaving only a 

 few remnants standing out in their original thickness, 

 where the strata were solid enough to resist the action 

 of the currents. Such are the hills of Monte Alegre, of 

 Obydos, Almeyrim, and Cupati, as well as the lower ridges 

 of Santarem. This escape of the waters did not, however, 

 entirely empty the whole basin ; for the period of denuda- 

 tion was again followed by one of quiet accumulation. 



