136 Reports & Proceedings — Geological Society of London, 



The gap left by the projection forward of the belt of seam is filled 

 with an unstratified sludge-like substance, commonly containing 

 angular masses of stratified argillaceous or arenaceous material. A 

 very finely-contorted specimen of sandstone from a true " wash-out" 

 shows quite plainly that the disturbance took place before the 

 material was indurated. 



In harmony with the contention that the overriding masses are not 

 due to tectonic " overthrusts " is the fact that reversed faults are 

 almost unknown in the coalfield, are never of considerable throw, and 

 many collieries have never seen one. 



In the roofs of many coal-seams and projecting slightly into the 

 coal are very curious roughly conical masses of sandstone, familiar to- 

 the miners as " drops " (or by other names) ; but these have, so far a& 

 the author knows, hitherto escaped 'notice by any geological writer. 

 They are commonly wrinkled on the surface as though partly 

 telescoped, and often have a flange on two sides, showing that they 

 were produced on the site of a crack. They are commonly ranged in 

 long rows. These the author interprets as casts of the funnel-shaped 

 orifices through which the sands surcharged with water have been 

 expelled, an invariable accompaniment of earthquakes in alluvial 

 tracts. The shape of these drops and their grouping negative the 

 idea that they are infillings of orifices occasioned by escapes of gas 

 arising from the decomposition of the peat. 



Fissures filled with sand or other materials, the "sandstone dykes" 

 of American writers, are not so common in the Midland Coalfield as 

 in some other coalfields, as, for example, Whitehaven ; but a number 

 exist. They show contortion where passing through the seam — 

 proving that the coal-substance had not undergone its full com- 

 pression at the time when the fissure was produced. 



Trough-shaped hollows, called "swilleys" or" swamps ", to which 

 some coal-seams are particularly prone, the' author attributes to 

 earthquake effects, such as the subterranean movements of sand, as- 

 quicksand. They are not tectonic, for exceedingly rarely, if ever, 

 is more than one seam on the same vertical affected. Sometimes the 

 formation of the swilley was coincident with the formation of the 

 seam, as is proved by changes within the trough in the nature of 

 the seam — particularly the occm-rence of cannel. 



All the phenomena here described were produced prior to the 

 production of the larger faults of this coalfield; but minor faults, 

 some affecting upper seams and not lower, others lower and not 

 upper, are probably to be attributed to earthquake action. 



A large number of examples of each type of phenomenon, drawn 

 from the examination of over thirty mines in the coalfield, are 

 discussed. . 



(2) "On Sandstone Dvkes or Rock-Riders in the Cumberland 

 Coalfield." By Albert Gilligan, D.Sc, B.Sc, F.G.S. 



The occurrence of these sandstone dykes was brought to the notice 

 of the author when engaged in investigations into the interruption s- 

 in the coal-seams of this area. They have been encountered at 

 various times in pits distributed all over the Coalfield; but those 



