19 u.] STEVENSON— FORMATION OF COAL BEDS. 109 



seen, often mark crises in accumulation of the mass. Not infre- 

 cjuently the sand and clay laminre of the roof disappear and the coal 

 is almost a solid layer, but evidence of unfavorable conditions still 

 remains in the high ash. 



At many localities the roof shale, composed of fine materials, 

 contains a profusion of plant remains, stems, fronds, leaves, retain- 

 ing the most delicate markings. Prostrate tree-trunks have been 

 traced in some cases scores of feet and twigs, with the branchlets 

 and leaves attached, have been found in considerable areas, the 

 fossils often as perfect as though they had been preserved in a 

 herbarium; the fronds of ferns at times show all parts in place and 

 as little disturbed as though they had fallen at the foot of the parent 

 plant. The whole arrangement indicates as gentle deposition of the 

 silts as that during overflow of the bottom swamps by muddy water 

 during rise of a Mississippi flood. But this is not always the condi- 

 tion. Renier^^*' states that one rarely finds in the Belgian coal fields 

 such remarkable specimens as are described as occurring in other 

 countries. For the most part, the plant remains are fragmentary. 

 So in the Appalachian basin; there are many localities where the 

 remains are beautifully perfect and there are many others in which 

 the remains, though retaining the delicate surface markings, are 

 fragmentary and distinctly not in place. The silts were not de- 

 posited as gently in some places as in others. Occasionally vertical 

 stumps are seen, with their roots spread out in normal position over 

 many square yards and still preserving the fragile rootlets, which 

 pass off in all directions as in a living plant. These erect trunks, 

 standing amid prostrate stems and vegetable debris, such as one 

 finds on the surface of forested swamps, rarely pass upward from 

 the coal. It is true that there would be difficulty in tracing the tree 

 downward in case the peat became structureless coal and that the 

 opportunity to make the effort -would be a rare one in a mine worked 

 for commercial output, but occasionally the exposure occurs and a 



"'A. Renier, "Observations paleoiitologiques sur le mode de formation 

 du terrains houillers beiges," Ann. Soc. Gcol. de Belgique, Vol. XXXII., 1904, 

 Mem., p. 261 et seq. 



