Sentence:  It is moreover certain that for eight or nine months of the year, the great rivers rush from their <WSD>gorges</WSD> into the mountains as torrents of clear water, or only, in the hot months, discoloured by fine glacial mud; [...] 
Meaning of the word marked with <WSD> tags:  A deep, narrow passage with steep, rocky sides, particularly one with a stream running through it; a ravine.