206 Dr. Mac Cullocli on the Lignites. 



other extremity of the series, scarcely differing from coal, and 

 finally identical with it. The term coal must therefore be taken 

 in a geological light, as applied to that substance in a particular 

 position, and not in a merely mineral sense. This seems the most 

 convenient arrangement, while it also corresponds with the views 

 of other geologists ; and thus every stratum or series, generally 

 considered as coal, which has been ascertained to lie in the strata 

 above the magnesian limestone, or red marl, will be here con- 

 sidered as lignite. 



While the superior antiquity of every lignite to peat, is proved 

 by the comparative nature of its geological position in all cases, 

 it is also inferred, from the more perfect change to bituminization 

 which the vegetable matter has undergone. And while the pro- 

 duction of the former appears to have ceased long ago, that of 

 the latter is matter of daily observation. 



Further, to prevent misapprehension respecting the meaning of 

 the term, under the name of lignite are here included, together 

 with all the coals just alluded to, those remains of trees or vege- 

 tables, which are buried under alluvial soil or very recent rocks, 

 and which combine, with remains of the vegetable structure more 

 or less perfect, marks of bituminization or charring ; which yield 

 bitumen, however modified, on distillation. Thus indeed, even, 

 the submerged wood which is found only under the very recent 

 alluvia, and which is more or less connected with peat, would be- 

 come necessarily included under that substance, whenever it cor- 

 responds in its chemical nature ; were it not more convenient to 

 distinguish it by geological characters, and to consider it a variety 

 of peat. 



The chemical nature of woody lignite will not perhaps be found, 

 in every instance, to correspond as precisely with its geological 

 position as, on this view, it should ; and it is also possible that 

 submerged wood may be so far bituminized as to be really undis- 

 tinguishable from it. This indeed ought to be the case, if the 

 gradation through the whole of these three combustible families 

 is perfect. If it be perfect, the difficulty of distinguishing them, 

 which would be the blemish of a mere arrangement, becomes 



