Among the remarkable phenomena which perhaps owe their existence to subterranean water-courses, we must mention the sudden or gradual appearance of those hillocks of clay (“mud-lumps”) which rise, to the great danger of navigators, either in the middle of the bar of the Mississippi, or in the immediate vicinity. Like small volcanoes of mud, the “mud-lumps” generally appear under the form of isolated cones, allowing a rill of dirty water to escape from their summits. Some of them are irregular on their surface, on which lateral orifices here and there show themselves, some in full activity, others abandoned by the springs which formerly gushed from them. The water of some “mud-lumps” is loaded with oxide of iron or carbonate of lime, which, with the agglutinated sands, form hard masses, having the consistence of perfect rocks. These hillocks vary both in their height and shape. The greater part remain hidden at the bottom of the water, and even their summits do not reach the level of the river or sea; others hardly raise their heads above the waves; the most considerable, however, rise to a height of 6, 9, or even 19 feet, and their base covers an area of several acres. The sudden way in which most of these water-volcanoes make their appearance, the anchors of vessels, and the remains of cargoes which have been found on their surface, their conical form, their terminal craters, and all the springs, “which seem to spout out as if from a subterranean sieve,” indicate the existence of a subterranean force always at work to upheave this band of hillocks. M. Thomassy is of opinion that the hillocks of these bars are the orifices of regular artesian wells naturally formed by a sheet of subterranean water descending from the plateaus of the interior and flowing below the Mississippi and the clayey levels of Louisiana. However this may be, the mode in which these mud hillocks are formed is well enough known to render it easy to clear them away from the mouths of the Mississippi and to protect the interests of navigation. When a cone of clay makes its appearance on the bar, a charge of powder is introduced into it and explodes it. Thus, in the year 1858, the southwest passage was cleared of a “mud-lump” which formed a considerable island; a single charge was sufficient to annihilate the whole. The island suddenly sunk; in its place a wide depression was formed, the circumference of which resembled that of a volcanic crater; at the same time an enormous quantity of hydrogen gas was discharged into the atmosphere.