1913-] STEVENSON— FORMATION OF COAL BEDS. 113 



rupted by ingress of marine conditions. The Harlem coal bed at a 

 locality in Ohio and at one in West Virginia has marine forms in the 

 upper part ; the condition is common enough in recent times ; Bel- 

 grand found a peat on the Seine which has many shells and passes 

 upward into a peaty clay and sand, full of shells; Yates described 

 a submerged forest in Cardigan bay where the stems of Pinus 

 sylvestris had been bored by Pholas and Teredo, after which the 

 peat-making was resumed. 



Barrois^-- classified the roofs which occur in a portion of the 

 Nord basin. He found, (i) sandstone, an offshore deposit, with 

 casts of trunks and branches of land plants; (2) shale with plants, 

 carbonaceous, remains abundant and well preserved, by their size 

 and distribution showing short transportation — they fell into the 

 mud from plants or were blown by the wind; (3) carbonaceous 

 shale, thin cannel-like, micaceous and pyritous, with remains of 

 fish — the water was brackish, marine or fresh, little disturbed and 

 deposition was slow ; (4) bituminous shale, brown, contains pelecy- 

 pods and crustaceans — thicker than 2 and accumulated more slowly 

 in fresh or brackish water, is often rich in fragmentary plant re- 

 mains and in fusain; (5) calcareous shale with marine shells, ac- 

 cumulated in deeper waters open to tides. Numbers i and 2, which 

 he terms Group A, are to be regarded as deposited by disturbed 

 water on a swampy surface, at times dry and never covered with 

 water more than 5 meters deep. The others, forming Group B, 

 were deposited in the deeper water of ponds, lakes, gulfs, as shown 

 by the finer grain and the association of plant remains with those 

 of animals. 



Erect trees, parallel among themselves, occur frequently in the 

 area examined. H these had been floated in from the land, they 

 should be found almost exclusively in roofs of Group B, deposited 

 in deep water ; on the other hand, they should be rare in Group A, 

 formed in shallow, muddy water, where they would be buried with- 

 out being able to retain the erect posture. But the studies show that 



"' C. Barrois, " La repartition des arbres debout dans le terrain houiller 

 de Lens et de Lievan," Ann. Soc. Geol. du Nord, Vol. XL., 1911, pp. 187-196. 



PROG. AMER. PHIL. SOC, LII. 2o8 H, PRINTED MAY 14, I9I3. 



