19"] STEVENSON— FORMATION OF COAL BEDS. 99 



brown and black coal on one side and the modern Flachmoor on the 

 other. The laminated structure is frequently present in peat. The 

 vast extent of some beds of comparatively pure coal cannot be 

 paralleled in recent autochthonous deposits, but the latter are of 

 great extent in some regions, whereas no extensive areas of alloch- 

 thonous carbon deposits are known to exist anywhere. He lays great 

 stress upon the occurrence of sub-surface parts of fossil plants in the 

 soils where they grew, the so-called petrified humus-soils. He 

 emphasizes especially the mode in which the Stigiiiaria rhizomas and 

 their appendices penetrate the underclay of coal beds, spreading out 

 and interlacing in such a manner that transport is inconceivable. 

 They must be in place. Equally conclusive are the modes in which 

 roots of Calaniariacccc rhizomas occur in the clays. This almost 

 universal underclay was the soil in which were rooted trees introduc- 

 ing the moor- formation. 



The occurrence of forest beds in stone- and brown-coal forma- 

 tion is not infrequent. He notes that at White Inch near Glasgow, 

 Scotland, and that near Senftenberg. Sometimes the profile is shown 

 in the roof ; sometimes there are successive forests embedded as 

 at Senftenberg, where erect stumps are associated with prostrate 

 trunks. These are conditions familiar to students of modern 

 swamps. The mode in which the Sfigmaricc have developed indi- 

 cates, in some localities, even the prevailing direction of the wind 

 at the time the trees grew. The growth of reeds in banks and the 

 parallel arrangement of their roots are the same in Mesozoic, Ceno- 

 zoic and recent deposits. 



Potonie carefully distinguishes the features of autochthonous de- 

 posits as contrasted with those of allochthonous origin, elaborating 

 the discussion given in the paper just cited. He states that Stig- 

 maria is not rare in the Commentry basin and that his search there 

 for that plant was rewarded abundantly. He discovered ' a fine 

 autochthonous stump, with spreading stigmarian rhizomas, still re- 

 taining the delicate appendices, the whole occupying a space of 6 

 meters diameter. He found there also a fern tree, almost com- 

 pletely preserved and with a frond attached to the stem. He con- 

 cludes that the condition must have been that of great quiet to 

 permit so nearly complete preservation. 



99 



