236 AMAZONIA AND LA PLATA. 



Eio Grande Lad liberated more than half, and in 1885 the anniversary of nation;! 

 independence was celebrated by the emancipation of 10,000. 



Physical Features. 



Rio Grande do Sul comprises four natural regions clearly indicated by the 

 general relief of the land. As in the neighbouring States, a " Piedmont " of 

 low lying coastlands stretches along the shores of the Atlantic, and these coast- 

 lands are separated, by a mountain range some 3,000 feet high from the inland 

 plateau sloping gently towards the Uruguay. But the coastland and coast range 

 are themselves separated by a deep depression in which the Rio Vacacah}-, con- 

 tinued by the Jacuhy, winds to the east, and the Ibicuy Grande, a tributary of 

 the Uruguay, to the west. 



The north-eastern section of the mountains preserves the name of Serra do 

 Mar, by which they are known as far north as Rio de Janeiro. But south of 

 the Rio Jacuhy the various sections take other names, such as Serra do Herval 

 between the Jacuhy and the Camacuam, and Serra dos Tapes thence to the Jaguarâo, 

 while various ridges bear other designations. As in the north, the system con- 

 sists of crystalline rocks, gneiss, and granites. 



In the transverse depression between the sea and the Uruguay is seen the edge 

 of the northern plateau standing out like the steep banks of a river, and this 

 scarp, presenting the aspect of a mountain on its outer face, generally takes the 

 name of Serra. It is decomposed into several groups, which become continuously 

 less precipitous in the direction of the west. The ridges branching off from the 

 Serra proper are known, like the southern heights near Uruguay, by the name 

 of coxiUias, " knives," although the crests, instead of being sharjD, are disposed in 

 long gently inclined slopes. 



In many places the primitive granites underlie layers of tertiary sands ; but 

 the relatively recent formations are chiefly represented by erupted traps, which 

 are easily weathered, taking a brown or yellow crust, and changing to that reddish 

 clay which covers nearly all the plains. In some of the central regions traps 

 occupy most of the surface, but they gradually diminish westwards in the direction 

 oE the Uruguay. Geologists generally associate with the presence of erupted 

 masses the transformation of argillaceous substances to agates, chalcedony, jaspar, 

 and amethysts, which occur in extraordinary quantities in some of the southern 

 districts. Besides these valuable stones Rio Grande also contains gold, silver, 

 copper, tin, lead, iron, kaolin, and coral. 



Coast Lagoons. 



The long beach developed in graceful curves along the Atlantic coast is 

 entirely of marine origin. This cordon of sands has been washed up by the waves 

 and modified with every tide by fresh deposits and fresh erosions. Various 

 phenomena point at a general upheaval of the outer beach itself, which now 



