Perhaps one of the reasons Humboldt had for believing the entire elevation of Jorullo to be due to the formation of a huge bladder was the fact that the plain on which the cone is situated, when struck, gave out a sound as though there was a vast hollow space below it. This was especially the case when the hoofs of the horses driven over its surface produced sounds as though they were moving over the summit of a hollow dome-like space below. But, as Lyell points out, this was probably only due to the fact that the materials forming the cone were very light and porous. According to Burkhardt, a German mining engineer who visited Jorullo in 1827, there appears to have been no other eruptions of the volcano since the time of Humboldt's visit. Mr. Burkhardt descended to the bottom of the crater and observed that small quantities of sulphurous vapors were still escaping. The small cones or _hornitos_, however, on the slopes had entirely ceased emitting steam. It appeared, too, that the twenty-four years that had passed since the time of Humboldt's visit, the rich soil of the surrounding country had permitted the successful cultivation of some crops of sugar cane and indigo. Russell appears to doubt the reliability of the information obtained by Humboldt concerning Jorullo. He suggests that a poetical account by the Jesuit missionary from whom Humboldt obtained much of his information was not apt to possess marked scientific accuracy. While, however, this may be true, yet to a certain extent it seems entirely probable that the principal facts were as above given. The following account as given by Humboldt, is taken from a translation made in the early part of 1800: "The affrighted inhabitants fled to the mountains of Aguasarco. A tract of ground from three to four square miles in extent, which goes by the name of Malpays, rose up in the shape of a bladder. The bounds of this convulsion are still distinguishable in the fractural strata. The Malpays, near its edge, is only twelve metres above the old level of the plain called the Playas de Jorullo; but the convexity of the ground thus thrown up increases progressively towards the centre, to an elevation of 160 metres (524.8 ft.).