19I3.] STEVENSON— FORMATION OF COAL BEDS. 49 



dozen failed to become distinctly red on burning. Those which 

 failed were mostly sandy and two of them were typical " fire-clays." 

 He has found that carbonate of iron frequently occurs as kidneys in 

 the mur — indeed he regards the presence of such kidneys as in some 

 way characteristic of the mur. The immediate provocation for 

 Stainier's discussion was the statement by Mourlon^*' that " the mur 

 represents the soil on which grew the now buried and metamorphosed 

 forests of the coal epoch. The forests then as now had the property 

 of taking away the iron disseminated in the soil." It is certain that 

 Mourlon and Dawson, in their generaHzed statement, have written 

 with too little reserve, for neither one of them could have intended 

 to assert that vegetation had removed all iron from the clay. One 

 reading Dawson's publications sees at once that he was familiar with 

 the occurrence of clay ironstone kidneys in underclays. Stainier says 

 correctly that, if coal be of in situ origin, the iron should be returned 

 to the soil when the trees die ; but it is evident that he reasons from 

 conditions existing in an upland forest, which are as a rule very 

 different from those upon which the in situ doctrine insists. Vegeta- 

 tion undergoing chemical change in swamps does not disappear but 

 becomes peat ; only a very small part of the inorganic matter could 

 find its way back to the mur ; it would remain in the peat. The mur 

 is merely the soil in which the vegetation began ; before long, the 

 decomposing plant material becomes the soil and all relation to the 

 mur ceases. The conception that trees cannot thrive in or on peat 

 is a curious survival, which retains its place in argument although it 

 is contrary to fact. As has been shown in an earlier part of this 

 work, the plant life of swamps is not confined to mosses and humble 

 plants but it includes large shrubs and great trees. Among the latter 

 are some of the noblest forms on the American continent, which 

 certainly thrive as well in swamps as on drier land. Very many 

 plants cannot live on the acid soil of peat, but there are very many 

 others which cannot thrive on soil of any other type. As will appear 

 on a later page, accumulation of peaty matter makes possible only 

 indirect action on the mur or original soil, and that is due only to the 



'" M. Mourlon, " Geologic de la Belgique," Bruxelles, 1880, Vol. I., p. 121, 



PROC. AMER. PHIL. SOC. , LII, 2o8 D, PRINTED MAY I3, 19X3. 



