It is interesting to know that the case supposed here has actually been realized in the delta of the Ganges. Some years ago an Artesian well was attempted to be made near Calcutta, and the auger was sunk to a depth of 481 feet.[71] The material passed through consisted of sand, clay, and nodules of argillaceous limestone, and at various depths, from 50 to 380 feet, several seams of decaying wood and peat were found, along with bones of various animals, such as deer and fresh-water tortoises, and fragments of lacustrine shells. Each of these vegetable layers evidently formed at one time a forest-covered swamp like those of the surrounding delta at the present day; and hence it follows, that during the accumulation of the Gangetic delta, the ground in that locality must have undergone a depression of more than 300 feet, and that this sinking has been interrupted by slight elevations, or by periods when the ground remained stationary, so as to admit of a dense and prolonged growth of vegetation, at successive intervals, upon the swampy flats and shifting islands. The general appearance of these old forests is pretty well shown by the mangrove swamps along the mouths of the river. These trees flourish in dense jungles on the banks, and extend even below high water mark, being covered in places by shell fish. So that were these maritime parts of the delta inundated by the ocean, and buried beneath a mass of mud and silt, the peaty layer that would be formed would display trunks of trees still occupying their original erect position, and spreading out their roots in the clay below, exactly as the sigillaria is found to do in the coal-seams of the carboniferous rocks, while clustered round the carbonized stems, or scattered among the decayed leaves and branches, there might be detected limpets and barnacles (as lingulæ and pectens occur in the coal-seams), showing, by their mode of occurrence, that they lived and died upon the spot. [Footnote 71: See Lyell's _Principles_, p. 280.]