430 Geological Society. 



fossil trees in the coal formation, which are thickened at their base, 

 and terminate in large expanding forked roots, to have been dicoty- 

 ledonous, whilst the monocotyledonous trees maintain throughout a 

 nearly uniform thickness, and their roots probably consisted of an 

 assemblage of succulent fibres ; and argues, that if beds of coal were, 

 like modern peat bogs, the accumulated remains of many genera- 

 tions of vegetables that grcM'' upon the spot, they may, during such 

 process of gradual accumulation, have afforded a surface adapted 

 for the growth of the trees in question. He attributes the fact of 

 the roots standing above the upper surface of the coal, as we some- 

 times see the roots of fir-trees above the surface of peat, to the 

 shrinking of the vegetable matter in which they grew, and considers 

 the actual thickness of each bed of solid coal to be about one-third 

 that of the vegetable mass from which it has been derived*. 



Mr. W. E. Logan has also communicated to us a series of minute 

 results of extensive examinations made by himself, and in many 

 cases confirmed by Mr. De la Beche, on the character of the beds 

 of clay immediately beloiv the coal seams in South Wales, from 

 which it appears that immediately beneath every bed of coal in 

 that extensive district is a substratum, called the tmderclay, varying 

 in thickness from six inches to more than ten feet ; and that this un- 

 derclay so universally and inseparably accompanies nearly a hundred 

 seams of coal throughout South Wales, that the collier seldom finds 

 coal where this substratum is wanting : it is usually a fire-clay, con- 

 taining sometimes an admixture of sand, and near Swansea passes 

 into a hard, fine-grained, siliceous sandstone. This never-failing sub- 

 stratum of the coal is everywhere characterized by the exclusive 

 presence of innumerable remains of Stigmaria Jicoides, the stems of 

 which are often of great length, and usually parallel to the plane 

 of the bed, and more abundant near the top than the bottom of 

 the underclay. From each of these stems there proceeds a series 

 of very long and narrow leaves, forming an entangled mass, which 

 traverses the fire-clay in every direction and to great distances ; 

 fragments of the stems of Stigmaria occur in other parts of the coal 

 formation, but in the underclay alone are the long thin leaves at- 

 tached to them. In 1818 the Rev. H. Steinhauer published in the 

 American Philosophical Transactions, vol. i. p. 273, a similar ac- 

 count of the occurrence in the English coal formation near Brad- 



* I wish to correct an error in my Address of last )ear (Phil. Mag., vol. 

 xvii. p. 512), where it is stated, that the place of the roots of the upright 

 trees discovered in the Bolton Railway was immediately under a thin bed 

 of coal ; the fact is, that they were all above this coal : the difference is 

 material, for if the roots be all above the coal seam, these trees, like fir-trees 

 in a peat-bog, may have giown upon the accumulating bed of vegetable 

 matter which is now converted to coal. 



The theory that coal, like peat, owes its origin to vegetables that grew on 

 the spot it now occupies, has been entertained by DeLuc, Macculloch, 

 Jameson, Brongniart, Lindley, and other writers, but I have nowhere be- 

 fore seen such convincing proofs of this hypothesis as are furnished by the 

 facts advanced by Mr. Hawkshaw, Mr. Bowman, and Mr. Logan, taken in 

 connexion with one another. 



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