1911 Encyclopædia Britannica, Volume 20… (1911)
“ On the western side these highlands terminate with a more or less sharply defined edge, the country sloping gradually up to their bases in gentle undulations with open, ill-defined valleys; on the eastern side they send out broad spurs enclosing deep-cut valleys, and the whole country retains more of an upland character. The tributaries that flow westward to the Paraguay are consequently to some extent navigable, while those that run eastward to the Parana are interrupted by rapids and falls, often of a formidable description. ”
