Theories of Formation of Coal, 111 



position of the alternating sandstones and shales in very shal- 

 low water ; and as we often find these rocks in regular thin 

 stratification, forming the immediate bottom of coal-seams, 

 the question arises, Could such a laminated arrangement of 

 detrital matter take place in water so shallow as is here sup- 

 posed % 



It is held by some geologists, that Stigmarue are the roots 

 of SigillaricB, and that the stems of the latter contributed 

 largely to the formation of coal. We should therefore ex- 

 pect to find, that where there is the greatest accumulation of 

 Stigmari(B there should be the thickest seams of coal : this is 

 not only not the case in the above sections, but sometimes 

 there is no coal at all (11, 12, e,fg^. In a bed of sandstone, 

 190 feet thick, in the South Wales section, and at a depth 

 within it of sixty feet, there is a seam of coal, four inches 

 thick, without underclay and without Stigmarice. Then 

 again, in the Novia Scotia section, we find stems of Sigillaricd, 

 standing at right angles to the plane of stratification, resting 

 on shales that do not contain any Stigmarm (i, ^, x, X, ^,). 

 Is this a proof that the stems are here, though apparently, 

 really not in the place where they grew 1 or is it a proof that 

 Stigmari(B are not the roots of SigillaricR ? 



Several instances of upright stems given in the Nova 

 Scotia section by Mr Logan, can hardly be considered as 

 occupying the spot where they grew, certainly not that (g) 

 where it is cut clean off at the bottom. It is remarkable, 

 that, in the instances of upright stems described by Mr Lyell 

 and Mr Logan, if occupying the spot where they grew, roots 

 should so seldom be connected with them. Of all parts of 

 the tree, none, we should expect, would be more likely to be 

 preserved ; being protected by their covering of soil from 

 causes of destruction to which the stems were evidently ex- 

 posed, as we find them so generally cut off at a short distance 

 above their bases. 



The whole subject of the theory of coal, whether we con- 

 sider its mode of deposition, the plants out of which it has 

 been formed, or the various changes which the vegetable 

 matter has undergone, to convert it into lignite, jet, common 

 coal, cannel coal, blind coal, and anthracite. Two or more of 

 these varieties often occurring in the same coal-field, is ex- 



