114 STEVENSON— FOR^IATION OF COAL BEDS. [April 21. 



such as appear in the basins of central France, which Fayol has 

 proved to be allochthonous. 



The deposits must have been made in shallow water ; Grand' 

 Eury has shown that the autochthonous flora of the Loire basin 

 could not have grown in water more than 10 to 15 meters deep. 

 There must have been a special combination of circumstances, since 

 *the deposits, in spite of the shallowness of the water, have in some 

 basins a thickness of some thousands of meters. This can be under- 

 stood if one accept a constant though variable subsidence through- 

 out the period of deposition. A certain instability of coast line in 

 paralic basins is proved by repeated inroads of the sea. If the sedi- 

 ments be laid down less rapidly than the surface sinks, marine con- 

 ditions prevail. Periods of rest, possibly of some elevation, would 

 be favorable to development of swamp vegetation, which, when sub- 

 sidence began again, would be buried under muddy and sandy depos- 

 its, until a new swampy area was produced, on which vegetation 

 began de novo. These movements can be followed with great clear- 

 ness in the Saarbruck and Loire basins. 



Similar movements in the period of man can be recognized along 

 many coasts. Dannenberg regards the Tertiary and Quaternary 

 history of the Netherlands as especially instructive. This he gives 

 in detail, showing that there have been successive advances and 

 retreats of the shore line, so that the section of Tertiary and Quater- 

 nary beds consists of sandstones, conglomerates, shales, marine beds 

 and peat deposits, wholly similar to the succession observed in the 

 Coal Measures. The filled river valleys observed in the Coal ]\Ieas- 

 ures, have their counterparts in these newer deposits. And it must 

 not be forgotten that, in the Carboniferous time, great orogenic 

 movements occurred, so that there was abundant material for filling 

 the basins. 



Stevenson,^^'' after studying the area, found himself unable to 

 accept Fa vol's conclusions respecting the mode in which the coal 

 beds were formed in the basin of Commentry. He agreed fully with 

 Favol as to the process by which the inorganic deposits were laid 



^'"J. J. Stevenson, "The Coal Basin of Commentry in Central France," 

 Ann. jY. V. Acad. Sci., XIX., 1910, pp. 161-204, 6 pi.; "The Coal Basin of 

 Decazeville, France," the same, XX., 191 1, pp. 243-294, 2 pi. 



114 



