Not unfrequently it happens that these strata of vegetable matter, with the roots and trunks of trees, their branches, fruits, and leaves, more or less perfectly preserved, are covered over by subsequent deposits. Such accumulations, we are assured by Doctor Mantell, have been found deep in the soil on the coast of England, in places that are still subject to periodical inundations. “The trees are chiefly of the oak, hazel, fir, birch, yew, willow, and ash; in short, almost every kind that is indigenous to this island occasionally occurs. The trunks and branches are dyed throughout of a deep ebony color by iron; and the wood is firm and heavy, and occasionally fit for domestic use; in Yorkshire and elsewhere, timber of this kind is sometimes employed in the construction of houses.”[63] Here, then, is the first stage of the conversion of wood into Coal,--a stratum more or less compacted together of vegetable matter, spread out sometimes over the surface of the dry land, sometimes on the floor of lakes and estuaries, and often buried beneath an accumulation of subsequent deposits. The next stage in the process of transformation may be represented by those Peat Bogs which constitute one of the most remarkable physical characteristics of Ireland, covering as they do an area equal to one-tenth of the whole island. In these the vegetable matter is more closely condensed, but the structure of the plants from which the Peat is derived is still preserved, and may be distinctly recognized by the naked eye. Nay, we have still the prostrate trunks of trees lying around on every side as they fell to the ground in their ancient forests. The researches recently pursued upon this subject have brought to light a fact which is very much to our present purpose; for it seems to prove our thesis by direct evidence. “In Limerick, in the district of Maine, one of the States of North America, there are Peat Bogs of considerable extent, in which a substance exactly similar to _cannel coal_ is found at the depth of three or four feet from the surface amidst the remains of rotten logs of wood and _beaver sticks_: the peat is twenty feet thick, and rests upon white sand. This coal was discovered on digging a ditch to drain a portion of the bog, for the purpose of obtaining peat for manure. The substance is a true bituminous coal, containing more bitumen than is found in any other variety. Polished sections of the compact masses exhibit the peculiar structure of coniferous trees, and prove that the coal was derived from a species allied to the American Fir.”[64] A similar phenomenon was observed by Doctor Dieffenbach in the Chathain Islands. In the same bed of peat he was able distinctly to trace a gradual transition from pure vegetable matter to a mineral substantially identical with common coal.[65]