Teneriffe, by Professor Smyth, ch. viii., and Humboldt, Voyage aux Régions Équinoctiales; Paris, 1814; i. 124.
They afterwards discovered smoke issuing from the centre of this patch of stones; so that volcanic heat may possibly have had something to do with the disappearance of the snow.
'Ce petit glacier souterrain,' Humboldt, l.c.
See p. 272 for an account of the underground glacier in the neighbourhood of the Casa Inglese.
Several of these caves are referred to by Reich, Beobachtungen über die Temperatur des Gesteins in verschiedenen Tiefen in den Gruben des Sächsischen Erzgebirges; Freiberg, 1834.