On the Formation of Coal. 179 



These observations of Dr Hooker rather, however, point 

 out the difficulties of explaining the origin of coal than re- 

 move them ; but are of great importance in showing that 

 some theories often proposed are not applicable, and thus 

 turniqg speculation into the right path. The climate of the 

 coal period has not been tropical, and this truth which the 

 shells preserved in the shales and limestones might long ago 

 have taught, is now confirmed also by the plants. It is not, 

 therefore, in internal heat, or in changes in the earth's axis 

 of rotation, that we have to look for the cause of our coal 

 beds. Rather, we suspect, will this be found in formations 

 like our actual peat mosses, and in a vegetation like that 

 which now flourishes on them, but of a larger size and more 

 rapid growth. And perhaps the difference in rapidity of 

 growth would be less than many think. Every moorland 

 farmer knows how soon the portions of peat cut out for fuel 

 are replaced by new moss, though we do not remember to have 

 seen any precise statement of the annual rate of increase. 

 We have little doubt that were this ascertained, the amount 

 of vegetable matter accumulated on an acre of surface by the 

 despised Sphagnum and its humble associates, would be found 

 far to surpass that produced in the same time by an equal 

 extent of ground covered by the stately oak or the lofty pine. 



When lately travelling across the Solway Moss by the 

 Caledonian Railway, we could not avoid feeling that in that 

 place we had before us some chapters in the history of a coal 

 formation, repeated in modern times. In the shallow cuttings 

 on the side of the line we see the undersoil of sand and gravel, 

 which may represent the sand>stones and conglomerates of 

 the ancient deposit. Then comes a thin bed of soil — a shale 

 or underclay — with roots of trees traversing it in all direc- 

 tions. Next is the modern coal, a thick bed of peat, full of 

 remains of trees — sometimes the whole stems prostrate along 

 the ground — sometimes the mere stumps still standing erect 

 in the place where they once flourished. Then often, above 

 all, we have another bed of shale, or clay and vegetable soil. 

 The surface, too, is as level as a coal deposit; and very 

 slightly elevated above the neighbouring Solway Frith. Sink 

 it but a few yards, and we might have the whole covered with 



