Until lately, the formation of the great cone of Jorullo was attributed to the same kind of action as the hornitos, but later travellers have established the fact that this is incorrect.

One of the De Saussure family, who was in Mexico a few years back, describes Jorullo as consisting of three terraces of basaltic lava, which have flowed one above another from a central orifice, the whole being surmounted by a cone of lapilli thrown up from the same opening, from which also later streams of lava have issued.
The celebrated cascade of Regla is just behind the hacienda.

There is a sort of basin, enclosed on three sides by a perpendicular wall of basaltic columns, some eighty feet high.

On the side opposite the opening, a mountain stream has cut a deep notch in this wall, and pours down in a cascade.

The basaltic pillars rest upon an undisturbed layer of basaltic conglomerate five feet thick, and that upon a bed of clay.
The place is very picturesque; and two great Yuccas which project over the waterfall, crowned with their star-like tufts of pointed leaves, have a strange effect.