From here the ascent is made on foot, and ever over the snow. The trail zigzags, because the slope is 24° or 25°, becoming more abrupt, until reaching 30° and 34°, at times. The walking is, naturally, very difficult. When some hundred metres have been traversed, great difficulty in breathing begins to be experienced, the lungs feel oppressed, and every step, every movement of the body, causes great fatigue and compels the stopping to take breath. Feeble constitutions cannot endure the weariness and illness which are experienced. The reflection of the sun upon the snow is intense, for which reason the wearing of dark glasses is necessary. The face should also be veiled, to prevent the vertigo, which the white sheet surrounding the traveler produces toward the middle of the journey; when the day is fine and the atmosphere clear, the panorama is incomparably beautiful. The city of Puebla is clearly seen, and, at a greater distance the peak of Orizaba and the Cofre of Perote. There may also be seen, with all clearness, the summit of Ixtaccihuatl, totally without a crater. After some four hours of travel, the end of the journey, the summit of the volcano is reached; the last steps are particularly difficult, because the slope is now 40° and the rarity of the air is greater; progress is difficult. From the point where the crater is reached it is not easy to take full cognizance of its depth, though the general form may be appreciated. This is elliptical; the major diameter measures some fifty metres more than the other. A crest of rock, of varying elevation, forms the edge, which makes it very irregular; it is very narrow; a simple step leads from the outer, to the inner, slope. This edge presents two heights--one is the _Espinazo del Diablo_ (Devil’s Backbone), the other is the _Pico Mayor_ (Greater peak), which is, as its name indicates, the highest point of the volcano, being 150 m. higher than the Espinazo. The _Pico Mayor_ is almost inaccessible, but its summit may, with difficulty, be reached. The major diameter of the crater corresponds to the two summits named, has some 850 m. length, and its direction is from south 20° west to north 20° east. The transverse diameter may be estimated at 750 m., which would give the crater a circumference of 2,500 m. In descending from the border, the crater presents three distinct parts; a slope of 65°, a vertical wall seventy metres in height, and another slope, which extends to the bottom. In total, the mean depth of this imposing abyss will reach 250 m. to 300 m. At the place, where the vertical wall begins and the first slope ends, there has been set up a sort of a windlass, below which an enormous beam slopes downward toward the abyss; by this beam, and lowered by a cord, the workmen who extract sulphur descend.