310 COAL. 



and origin of all the modes of coal. But that com- 

 parison could not now be drawn without anticipating 

 the history both of peat and lignite ; and I shall there- 

 fore defer it till that of peat has been given. 



The organic substances connected with coal, are, 

 very predominantly, those of vegetables; as to the last 

 it is indebted for its origin. In some instances, shells 

 occur; as in Derbyshire. While some of these un- 

 questionably belong to fresh water, many are doubt- 

 ful, and others are thought as certainly to be marine. 

 The genera Ammonite's, Orthocera, Mytilus, Unio, 

 Terebratula, and Lingula have been remarked, among 

 others ; and even the fragment of a fish has been 

 observed. 1 have elsewhere pointed out the difficulty 

 of pronouncing respecting the exclusive origin of any 

 shell; though there is nothing in the theory of coal 

 that should absolutely exclude marine remains. The 

 most perfect vegetable remains are found in the shales, 

 though they occur also in the sandstones. Yet if coal 

 often contains carbonized wood, or portions of plants, 

 of which the interior organization is sometimes visible, 

 or so abounds in charcoal that it pervades the whole 

 mass, this will, I believe, be found the case rather in 

 the superior, or lignite coals, than in the series under 

 review. 



The progress of fossil botany is as yet so imperfect, 

 and those remains are often so broken and obscured, 

 that not much has been done towards their effectual 

 description and arrangement. For that information 

 which does not fall within the plan of this work, the 

 reader must be referred to Sternberg, Schlottheim, 

 Brongniart, and others, or to the abstract of Cony- 

 beare and Phillips. It is sufficient to remark, that 

 plants of aquatic habits seern to prevail among them ; 

 the predominant remains being those of gigantic vege- 



