The pick advances laboriously through the calcareous layers alternating with very slender threads of clay, and schistose beds in plates incrusted with oyster-shells, the contemporaries of the pre-Adamite oceans. Sometimes a rivulet suddenly bursts through a vault that has been begun, and inundates the laborers; or a layer of marl is laid bare, and rolls down with the fury of a cataract, breaking the stoutest supporting beams like glass. Quite recently, at Villette, when it became necessary to pass the collecting sewer under the Saint-Martin canal without interrupting navigation or emptying the canal, a fissure appeared in the basin of the canal, water suddenly became abundant in the subterranean tunnel, which was beyond the power of the pumping engines; it was necessary to send a diver to explore the fissure which had been made in the narrow entrance of the grand basin, and it was not without great difficulty that it was stopped up. Elsewhere near the Seine, and even at a considerable distance from the river, as for instance, at Belleville, Grand-Rue and Lumière Passage, quicksands are encountered in which one sticks fast, and in which a man sinks visibly. Add suffocation by miasmas, burial by slides, and sudden crumbling of the earth.