C— GEOLOGY. G9 



for 210 feet is compensated for by only 35 feet of excess on tlio 

 margin. 



Seismic Phenomena in the Seams. 



While the displacements and duplications are totally unlike those 

 produced by faults, there are cases in which the seam appears to have 

 been subjected to a stretching tension and to have broken under tlie 

 strain. Along the zone of such a stretch great confusion is commonly 

 found. Masses of sedimentary materials of the coal seam, and slabs 

 and seams of cannel commonly occur, besides a curious argillaceous 

 substance unlike any natural rock with which I am acquainted. In 

 its unstratified structurelessness it suggests a kind of consolidated sludge 

 such as might be produced by violently stirring or shaking a quantity 

 of not too liquid mud. Where the seam abuts against this stuff it 

 presents usually a nearly vertical ragged edge, its bright and dull layers 

 preserving their characteristics quite up to the contact. 



Masses of the seam enclose streaks of sandstone or muddy material 

 along the bedding planes, and plates of sandstone descend in tortuous 

 folds in the body of the seam. Sometimes ' eyes ' of sandstone are 

 seen embedded in the coal without any visible feeders, though in mosi 

 cases the feeders, even almost hair streaks, can be discerned. 



In many instances the sandstones in a wash-out of this type are 

 found to be in great boat-bottom rolls, and even the whole sedimentary 

 contents of the wash-out may lie in recumbent folds. The degree in 

 which these disturbances are developed varies extremely; for example, 

 at Shirebrook and Steetley Collieries there is no complication of any 

 description either in the seam — the Top Hard or Barnsley Bed — or on 

 the margins of the infilling of the 'wash-out.' At Manton, probably 

 on the samie wash-out, not more than two miles away, though there 

 is only a small amount of swelling of the seam on the margin and a 

 little injected sandstone in the coal, the filling of the wash-out v/as for 

 some distance in perfectly horizontal recumbent folds of more than the 

 full height of the workings. In this case it is interesting to observe that 

 there were many tree-trunks represented by bright coal of great bril- 

 liance, and I observed one large Calamite standing in the position of 

 growth in the undisturbed material of the filling. 



I would illustrate by a concrete example — the great ' wash-out 

 represented by the Haigh Moor Eock is accompanied by a disturbance 

 of the seam of portentous magnitude. In a range of four coterminous 

 collieries the seam exhibits dislocations and over-riding repetitions and 

 other anomalies along a general S.W.-N.E. hne, coinciding roughly witli 

 the course of a normal steep hading fault of considerable magnitude. 

 In many places the disturbance just along its edge culminates in over- 

 ridings and repetitions whereby the thickness of the seam is increased 

 from the normal 4 feet 6 inclies up to 15 and 16 feet in some places, but 

 this excess of coal is restricted to a- narrow belt, while the default 

 extends to scores or even to hundreds of yards. 



That there is a connection between wash-outs and tectonic features 

 I have long believed, and I pointed out some seventeen years ago' that 



7 Quart. Jour. Gaol. Soc, vol. Ixi., p. 344. 



