As we advanced the Mal Pais became more broken: the 'bad step' was ugly climbing, and we often envied our men, who wore heelless shoes of soft untanned leather with soles almost as broad as they were long. The roughness of the trachytic blocks, however, rendered a slip impossible. At 6.45 we reached the second floor of this three-storied volcano, here 11,721 feet high. The guides call it the _Pico del Pilon_, because it is the ancient Peak-Crater, and strangers the Rambleta (not Rembleta) Volcano, which strewed Las Cañádas with fiery pumice, and which shot up the terminal head 'conical as a cylinder.' It has now become an irregular and slightly convex plain a mile in diameter, whose centre is the terminal chimney. Its main peculiarity is in the fumaroles, or escapes of steam, and _mofetti_, mephitic emanations of limpid water and sulphur-vapour. Of these we counted five narices within as many hundred yards. Their temperature greatly varies, 109° and 158° Fahr. being, perhaps, the extremes; my thermometer showed 130°. These _soupiraux_ or _respiradouros_ are easily explained. The percolations from above are heated to steam by stones rich in 'grough brimstone.' Here it was that Humboldt saw apparent lateral shiftings and perpendicular oscillations of fixed stars; and our Admiralty, not wishing to be behind him, directed Professor P. Smyth's attention to 'scintillations in general.' Only the youngest of travellers would use such a place as an observatory; and only the youngest of observers would have considered this _libration of the stars_ an extraordinary phenomenon. Directed by a regular line of steam-puffs, we attacked _El Pilon_, the third story, the most modern cone of eruption, the dwarf chimney which looks like a thimble from the sea. The lower third was of loose crumbling pumice, more finely comminuted than we had yet seen; this is what Humboldt calls 'ash-cones.' There was also a strew of porphyritic lava-chips covered with a red (ochreous?) crust. Presently we reached a radiating rib of lately ejected lava, possibly the ridge of a dyke, brown below and gradually whitening with sulphuric acid as it rose towards the crater-walls. The resting took longer than the walking up the steep talus; and at 7.45: after a total of nine hours and a morning's work of two hours and a half, which occupied two in descending, we stood upon the corona or lip of 'Teyde.'