Sentence:  In western Europe, the most celebrated instance of the <WSD>occultation</WSD> of a river "was" that of the Rhone, near Bellegarde, on the confines of France and Savoy, about 18 miles from Geneva; but, alas, on visiting this interesting spot in the autumn of 1855, I found that the "Perte du Rhone" no longer exists; for the Sardinian Government, in which territory it was, had blown up the rocky roof, beneath which it had been engulfed, in order to facilitate the conveyance of timber on the river. 
Meaning of the word marked with <WSD> tags:  The state of being (hidden, undetected).