COAL: ITS STRUCTURE AND FORMATION. 365 



to regard them as unknown forms of plant life proved too 

 strong, and they were all laboriously figured and defined as 

 new types of protophytic genera. The majority of Reinsch's 

 genera must be regarded as inorganic structures, whilst others 

 are clearly founded on plant tissues or spores. In addition 

 to various fragments of vascular tissue he recognised several 

 spores, and to these applied the generic term, Triletes, 

 which some authors have found convenient. Following 

 these investigations we have a paper by Fischer and Riist, 

 in which Reinsch's conclusions are called in question, and 

 the various strange " plants " are regarded as examples of 

 the numerous forms assumed by resinous and other sub- 

 stances which enter into the composition of coal. The 

 same observers mention the occurrence of several definite 

 crystalline substances in certain forms of coal, e.g., 

 Fichtelite, Hartite, etc. A detailed account of such bodies 

 in coal rocks, and of the various forms of coal, lignite, etc., 

 has lately appeared in the third volume of Zirkel's new 

 edition of his Lehrbuch der Petrog?^apkie. In 1883 Gumbel 

 published a valuable account of the minute structure of coal, 

 lignite, and peat ; his method of examination is fully de- 

 scribed, and the results obtained bear out the advantage of 

 a chemical treatment in certain cases. He points out that 

 Reinsch included in his protophytic genera such structures 

 as dendritic crystals of sulphur, and various other mineral 

 substances. The same author treats of the method of con- 

 version of plant tissues into coal, and disputes the accuracy 

 of the common statement that anthracite is simply coal 

 which has been subjected to greater pressure. The occur- 

 rence of anthracite not merely in the deeper layers of a coal 

 series, but between or above ordinary beds of coal, suggests 

 some other factor than increased pressure and metamorphism. 

 In discussing the question of coal formation, Gumbel recog- 

 nises that there must have been different methods by which 

 the same results were obtained ; but, on the whole, he is 

 disposed to agree that there are good grounds for the com- 

 parison of Palaeozoic coal seams and modern peat formations. 

 The important memoir on coal by Grand' Eury 1 contains 



1 Grand' Eury (1). 

 26 



