60 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



did not grow sur place. Since the rapid current, which piled sand 

 around the forests of Treuil, did not uproot the trees, one finds 

 difficulty in understanding how the waters so slightly agitated as to 

 be able to draw off only leaves and twigs did not leave in place the 

 stumps whose roots are seen to-day in the underclays. 



The preservation of the underclay proves that the stumps were 

 not torn out before deposit of the plant debris forming the coal bed. 

 The clay shows no signs of erosive action such as are seen so often 

 in the roof. The deposit of the clay is itself a proof that then had 

 begun the long period of tranquillity, which continued during forma- 

 tion of the coal. He is convinced that it must be admitted as almost 

 proved that the coal beds have come from a vigorous local vegeta- 

 tion, whose debris accumulated at the bottom of shallow stagnant 

 water and probably, quite as often, on a damp but not flooded 

 surface. 



The intervening rocks are, in character, wholly similar to part- 

 ings in the coal beds, but they were formed not by petty inundations 

 but by strong currents of prolonged duration. The existence of 

 these is proved by erosions as well as by the sands which covered 

 the coal forests. The surface subsided at intervals, as shown by 

 phenomena connected with the faults in the Loire basin. But the 

 flora was not destroyed, for one finds forests or isolated trees in 

 place, in sandstones at all horizons, their bark preserved as coal. 

 The sands are evidence that the agitated water prevented quiet depo- 

 sition of vegetable debris. That was destroyed or scattered afar. 



Meanwhile, the sunken surface was leveled up and the depres- 

 sion was filled. A second marsh was formed above the first, now 

 buried under a thick bed of sand or mud. If the deposit of sand, 

 etc., did not exceed 30 meters, the conditions under which the new 

 bed was formed might not differ from those of the earlier bed. But 

 when the sterile interval attains great thickness, 100 to 800 meters, 

 the period of depression was very long and before its close the flora 

 had undergone modification. Thus it is that one finds successive 

 appearance of varied types, so that classification of the Coal ]\Ieas- 

 ures by their flora becomes possible. Subsidence of the type here 

 conceived has been observed in rocks of all epochs. Lament and 



