Hemp to Hydro-electricity

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In 1867, explorer Richard Burton canoed the length of the previously uncharted São Francisco river in Brazil scouting for the British empire. BBC Brazilian journalist Paulo Cabral retraces the route, recording his own 21st-century impressions of life there. Third and final part: from the notorius "marijuana polygon" near Cabrobó to the once-great waterfalls at Paulo Afonso.