112 STEVENSON— FORMATION OF COAL BEDS. [April iS. 



from Iowa and Indiana ; Tschernychew and Loutougin^-° state that 

 four coal beds in the Donetz basin of central Russia have marine 

 limestone or calcareous shale as the roof material. Coals of the 

 Monongahela and higher formations frequently have non-marine 

 limestone as the roof material. Lipoid has shown that the Triassic 

 coals of his area sometimes have shale but at others limestone roof. 

 Von Giimbel and de Serres have described beds of lignite with lime- 

 stone roof. Peat deposits have in most cases either clay or sand 

 roofs but calcareous roofs have been recorded on a preceding page. 



Occasionally a coal bed is found between marine limestones. 

 Fayol saw at Fontaine near Mariemont in Belgium two beds of 

 anthracite, 3 meters apart, intercalated in marine calcareous shale. 

 He thinks that, according to the in situ theory of origin, it would be 

 necessary to suppose that the lower limestone, produced in deep 

 water, was lifted and emerged ; then that a submergence of similar 

 amplitude occurred after formation of the first coal bed; that a 

 second emergence succeeded the deposit of 3 meters of limestone 

 and that a second submergence followed formation of the second 

 anthracite bed. Be that conclusion good or not, it is certain that 

 occasionally a coal bed is seen in contact with marine limestone 

 above and below ; Illinois Coal VI. not infrequently has this feature, 

 though it must be said that in areas of hundreds of square miles it 

 is separated by several feet of clay below and of shale above. The 

 Tertiary coal at Haring, as well as some south Bavarian coals of the 

 same age, is said by von Giimbel to be between limestones : he thinks 

 that the former was a cedar swamp. Virlet d'Aoust'-' has described 

 the section exposed in a great excavation east from Havre. He 

 saw there 3 characteristic beds of peat, which are merely intercala- 

 tions in a mass of very calcareous clay, containing abundance of 

 marine shells belonging to Cardium, Mytilus and other genera. 



It is quite possible also for accumulation of coal to be inter- 



'-' Th. Tschernychew and L. Loutougin, " Le bassin du Donetz," Guide 

 des Excur. Vllme Cong. Geol., 1897, XVI., pp. 13, I4- 



''* Virlet d'Aoust, " Note sur le terrain d'atterissements recents de I'em- 

 bouchure de la Seine," Bull. Soc. Gcol. de France, II., Vol. VI., 1849, pp. 

 606-625. 



