180 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



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 supposed ? 



It is held by some geologists, that Stigmarice are the roots of 

 Sigillarice, and that the stems of the latter contributed largely to 

 the formation of coal. We should therefore expect to find, that 

 where there is the greatest accumulation of Stigmarice 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,fy g). 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 Nova Scotia section, we find stems of Sigillaria^ 

 standing at right angles to the plane of stratification, resting on 

 shales that do not contain any Stigmarice (i, ^, k, X, /x). Is this a 

 proof that the stems are here, though apparently, really not in the 

 place where they grew ; or is it a proof that Stigmarice are not the 

 roots of Sigillarice ? 



Several of the instances of upright stems given in the Nova Sco- 

 tia section by Mr. Logan, can hardly be considered as occupying 

 the spot were they grew, certainly not that (^) where it is cut 

 clean ofi* 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 

 exposed, as we find them so generally cut ofi" at a short distance 

 above their bases. 



The whole subject of the theory of coal, whether we consider 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 extremely obscure, and presents a wide and interesting 

 field for future investigation. Before concluding this part of my sub- 

 ject, into which I shall probably be thought to have entered at dis- 

 proportionate length, I would call your attention to some difficulties 

 which the South Welch section offers to the commonly-received and, 

 I believe, well-founded opinion, that anthracite is bituminous coal, 

 the volatile parts of which have been driven off by heat acting gra- 

 dually from below ; for we see (8 and 9) that thin seams of com- 

 mon coal are interstratified with anthracitic seams and with anthra- 

 cite. Neither do we find any signs of metamorphic action in the 

 underclay in immediate contact with the coal, nor in the strata that 

 lie between two seams of anthracite. We must look to the chemist 

 to explain all this, as well as for enlightenment on the formation of 

 the different qualities of coal ; but we must be contented to receive 

 from him only indications and resemblances ; for we must never 



