Among other objects of curiosity, which can only be illustrated by particular description, are the explosions of mud, situated between the district of Grobogan on the west, and of Blora and Jipang on the east. By the natives they are termed Blédeg, and are described by Dr. Horsfield as salt wells.
"These salt wells," he observes, "are dispersed through a district of country several miles in circumference, the base of which, like that of other parts of the island which furnish mineral and other saline waters, is limestone. They are of considerable number, and force themselves upwards, through apertures in the rocks, with some violence and ebullition. The waters are strongly impregnated with sea-salt, and yield upon evaporation very good salt for culinary purposes. (In quantity not less than two hundred tons in the year.)
"About the centre of this limestone district, is found an extraordinary volcanic phenomenon. On approaching it from a distance, it is first discovered by a large volume of smoke rising and disappearing at intervals of a few seconds, resembling the vapours arising from a violent surf: a dull noise is heard, like that of distant thunder. Having advanced so near, that the vision was no longer impeded by the smoke, a large hemispherical mass was observed, consisting of black earth, mixed with water, about sixteen feet in diameter, rising to the height of twenty or thirty feet in a perfectly regular manner, and as it were pushed up, by a force beneath; which suddenly exploded with a dull noise, and scattered about a volume of black mud in every direction. After an interval of two or three, or sometimes four or five seconds, the hemispherical body of mud or earth rose and exploded again. In the same manner this volcanic ebullition goes on without interruption, throwing up a globular body of mud, and dispersing it with violence through the neighbouring plain. The spot where the ebullition occurs is nearly circular and perfectly level, it is covered only with the earthy particles impregnated with salt water, which are thrown up from below; the circumference may be estimated at about half an English mile. In order to conduct the salt water to the circumference, small passages, or gutters, are made in the loose muddy earth, which lead it to the borders, where it is collected in holes dug in the ground for the purpose of evaporation.