242 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



pressure. A considerable loss of substance takes place during 

 the transformation ; Bischof reckoned that a mass of plant 

 material about eighty feet thick will only yield a coal-seam 

 about three feet in thickness. 



There still continues a difference of opinion whether black 

 coal originated in situ or if the plant material had been drifted and 

 deposited in the same way as other sedimentary rock. Lyell, 

 Logan, Goeppert, Giimbel are among the geologists who sup- 

 ported the view that the transformation of the vegetable matter 

 took place in situ, as in the case of the large proportion of 

 peat-mosses, and this is the common opinion of geologists. 



In France, however, the theory of sedimentation is strongly 

 supported. Grand-Eury, the author of an excellent work pub- 

 lished in 1882, upon the flora of the Carboniferous formation 

 of Central France, came to the conclusion that the coal-seams 

 had originated by deposition in lake-depressions surrounded 

 by woods. Five years later, the Etudes of Henry Fayol 

 on the Coal-deposits of Commentry brought forward a strong 

 chain of evidence in favour of sedimentation from water. 

 Fayol shows how the pebbles, sand, mud, and plant detritus 

 borne in suspension by rivers subside according to their weight, 

 and arrange themselves as independent layers of sediment. 

 The coarser pebbles are deposited near the shore, usually with 

 a distinct slope, while the light plant detritus is carried far out 

 and deposited almost horizontally. 



In accordance with the amount of rainfall, the volume 

 and velocity of the inflowing water vary, likewise the erosive 

 action of rain and river water and the quality of the sediments. 

 So that the alternation of conglomerate, sandstone, shale, and 

 coal-seams observed in most coal-basins finds, according to 

 Fayol, a natural explanation upon the basis of increase and 

 decrease of rainfall without assuming oscillations of ground- 

 level as has been done by the supporters of the coal-swamp 

 theory of origin. 



De Lapparerit has not only. accepted the views of Fayol and 

 applied them generally to coal-basins, but also supported them 

 by further arguments. It is in no small measure due to the 

 prestige of this gifted geologist that the sedimentation theory 

 is held by the majority of French geologists at the present 

 day. A slight modification of the theory was recently advanced 

 by Ochsenius (1892), who suggests that river-bars controlled 

 the admission of the inflowing water into the lake-basins, 



