454 ORIGIN OF THE APPALACHIAN COAL STRATA, 



ical importance of this generalization concerning the Stigmaria, 

 and the fire-clay inclosing it, appears to have been discerned 

 by M\: Logan, but he Ijas not offered any explanation of 

 the fact. The following passage, from the published absti-act of 

 his paper, conveys his views : " When it is considered, that over 

 so considerable an area as the coal-field of South Wales, not a 

 seam lias been discovered, williout an under-clay abounding in 

 Stigmaria, it is impossible to avoid the inference, that there is 

 some essential and necessary connection between the existence 

 of the Stigmaria and the production of the coal. To account for 

 their unfailing combination by drift, seems unsatisfactory ; but 

 whatever may be the mutual dependence of the phenomena, it 

 affords reasonable grounds to suppose, that the Stigmaria ficoides 

 is the plant to which we may mainly ascribe the vast stores of 

 fossil fuel." I am not aware, that either ]Mi-. Logan, or any other 

 geological writer, has attempted to account for the great frequen- 

 cy of this sti'atum immediately underneath the coal, or that any 

 hypothesis has been advanced to explain the general prevalence 

 in it of the Stigmaria, and the absence of all those other species of 

 plants, which abound among the layers of the coal itself, and in 

 the roof, and other overlying rocks. One main object of the fol- 

 lowing theory of the origin of the coal-measures, is to attempt the 

 solution of these curious facts : * 



* Since this memoir was written, my attention has been called by my brother. Prof. 

 Wm. B. Rogers, of Virginia, to the splendid work of Mr. Edward ^Mammatt, on die Coal- 

 Field of Ashby de la Zonch, published in 1S.34. This elaborate description contains a 

 clear announcement of an under-clay for almost every coal-seam, and mentions, more- 

 over, the presence " of a distinct single vegetation " in that of the main coal, with other 

 facts and suggestions, since confirmed by Mr. Logan, and several other recent writers, 

 on the origin of the coal strata. I cannot find, that the obvious claims of Mr. Mammatt 

 to priority, as a discoverer in this interesting subject, have been any where acknowl- 

 edged. It is to be regretted, that the still earlier opinions of Werner, De Luc. and Adolpli 

 Brongniart, attributing the vegetable matter of the coal-beds to a growth on the spot 

 where the coal now exists, should have escaped so generally the attention of British ge- 

 ologists, with the exception of Mr Lyell * 



The following passages, from Mr. Mammatt"s work, will convince us how ver^' near 

 he was to a clear conception of the relations of the Stigmaria, and to a sound doctrine of 

 the circumstances, under which the coal-beds were accumulated. " Seams of fire-clay 

 abound in the Ashby coal-field, and there are very few coal-measures (coal-seams ?) which 



• Since thi« paper wa» read, Dr. Buckland'i admirable ' Annivenary AddreM to the Geol. Society of London, for 1841,' bat 

 appear<!d ; in which he mrntionn, that Ihii doctrine hai been entertained bvDe Luc, McCulloch, Jameson, Bronfniart, Lindley, 

 and other writera. 



