446 STEVENSON— THE FORMATION OF COAL BEDS, l^'ov. i, 



effects of a water current are seen in the Forest of Dean, where 

 a coal seam, 5 to 6 feet thick, was washed out in one portion of the 

 colliery and redeposited in another, where it is 8 to 12 feet thick. 

 The character of the pehbles led him to the conclusion that the coal, 

 prior to deposition of roof materials, " was to great extent con- 

 solidated though perhaps only partially indurated." 



In discussing this paper, Moggridge stated his belief that the 

 pebbles were derived from broken up coal beds, the debris being 

 distributed in the newer deposits. There is a bed of good cannel 

 only 4 miles from Penslawdd, so that one need not look far for the 

 source, the more so since the cannel is at greater altitude. Morris 

 thought the pebbles derived from one of three sources ; they might 

 be fragments of floating wood encased in sandstone and carbonized, 

 they might come from the breaking up of submerged forests, whose 

 fragments became embedded in sands and clays, or from the break- 

 ing up of coal beds. Jordan could not accept Moggridge's sug- 

 gestion, because the present greater altitude of the cannel bed is 

 due to late movements, or those of jNIorris because the pebbles are 

 confined to sandstone roofs and are not distributed throughout the 

 series. 



It is well to introduce here, in advance, notes having some bear- 

 ing on the matter in hand, though more upon another, which will 

 be considered in connection with coal beds themselves. Stevenson^^ 

 found coal fragments in a sandstone overlying the Pittsburgh coal 

 bed. At one locality, the lower layers " contain lumps of coal, 

 coarse pebbles and fragments of vegetable stems, the whole looking 

 as though its deposition was accompanied by enough disturbance to 

 tear off part of the old swamp. It is clear, however, that not all of 

 the fragments found in the stratum belong to the same bed. Some 

 of them are crushed and fractured in such manner as to show that 

 they were consolidated before removal, while others are saucer- 

 shaped." He thinks that the latter came from the Pittsburgh coal 

 bed and that the others were derived from an older bed, outcropping 

 at some distance eastward. At another locality, the derivation is 



" Sec. Geol. Surv. Penn., Report K, 1876, pp. 90, 137. 285 ; Report KKK, 

 1878, pp. 79, 81, 87, 118. 



