66 SECTIONAL ADDRESSES. 



but in this instance there are additional features of extraordinary interest 

 and significance. The channel is filled mainly with two beds of anthi-a- 

 citic coal, one below and the otTier above a lens of black shale. The 

 fact that this anthracite is devoid of underclay and that it yields remains 

 of fishes and amphibia at once declares it to have originated as cannel, 

 which I have found to be a usual component of these lenses. Just 

 outside the channel the section at the pit bottom shows 4 inches of coal 

 resting upon an underclay and overlain by coarse sandstone, showing 

 that this is a relic of the original seam, but it must have been largely 

 destroyed by a later incursion of the stream which laid down the 

 sandstone. 



The split in the Middleton Main Coal must be regarded as a silted 

 chajinel of a river that traversed the swamp after the formation of the 

 lower part of the seam, and, as might be expected, evidence is abundant 

 of similar stream action in other phases of the Coal Measure deposition. 

 In the shales intervening between the seams belts of strongly current- 

 bedded sandstone with the transverse section of an infilled trough are 

 often to be found. Small examples are now to be seen in the railway 

 cutting just east of Leeds on the line to Hull; and in Altofts Colliery, 

 Fox Pit, a similar trough has been traced in the roof of the Middleton 

 Main seam for a distance of about half a mile. In this instance it is 

 probable that the direction in which the water was flowing is indicated 

 by the fact that in the N.E. woi'kings the floor of the trough is 

 wholly above the seam, while in the S.W. it is cut into the seam to a 

 depth of about a foot. When a seam is more deeply eroded the only 

 too familiar phenomenon of a ' wash-out,' in the miner's sense, not in 

 that of the modern colloquialism, is formed. We should expect such 

 a deltaic area to afford evidence of the actual meanderings of the main 

 stream, or of its more or less transient tributaries or distributaries. 

 These are most easily recognised by the channels which they cut in 

 the new-formed deposits. 



Extensive beds of gravel or conglomerate are of very exceptional 

 occurrence, the source of the materials being in general so remote and 

 the grade of the rivers so low that such deposits would hardly be 

 expected unless the tearing up of the new strata could furnish them — 

 as we shall see that in some cases they did. The lesser ' wash-outs ' 

 may be the effects of transient streams which swept across the shallow 

 mud-floored lagoons, cutting out a channel and later silting it up. 



Such rivers, contemporary and sub-contemporary with the formation 

 of the coal, show the ordinary complications inseparable from river 

 erosion. They meander on a large scale; the bows are frequently 

 found to be subjected to ' cut-offs,' and in such cases the 'oxbows' 

 frequently contain beds of cannel, speaking of their existence as a stag- 

 nant bayou in which vegetable mud accumulated. They exhibit the 

 ])henomena of 'cut within cut,' consequent upon rejuvenescence or 

 the scour of flood waters, and the margins are often affected by the 

 falling in of the banks. These are quite ordinary phenomena connota- 

 tive of the action of moving water. 



A typical ' wash-out '' occurs in the Parkgate seam at Aldwarke 

 and Eotherham Main Collieries Here a mass of sandstone cuts out 



i 



