Abstract
LONDON. Geological Society, January 8.—Mr. G. W. Lamplugh, president, in the chair.—Prof. P. F. Kendall: “Washouts”in coal-seams and the effects of contemporary earthquakes. Two types of interruptions are differentiated in coal-seams which have been confused under the general terms of “wash-outs,”“wants,”“nips,”or “dumb-faults.”One type may be due to erosion by contemporary streams which coursed through the alluvial area where the coal material was accumulating. A number of examples of this type in the Midland coalfield are described. Split seams of the type in which the seam rejoins are kindred phenomena, but in these cases the erosion was always contemporary. Great diversity in the phenomena of splits and wash-outs arises from the differences in the ratios of shrinkage during consolidation of the various constituents. Catinel acts as a substance of little compressibility, Other disturbances of the coal-seams, miscalled “wash-outs,”are referred to earthquakes. Some of the effects, of earthquakes in Coal Measure times might be expected to be of a magnitude greater than the effects of recent earthquakes. An abnormality in coal-seams consists in the intrusion into the coal of sedimentary material or the encroachment off masses of amorphous sandstone as “rock-rolls,”probably due to the invasion of sands rendered mobile by excess of water, and perhaps of gas, and moving under the impulse of waves of elastic compression produced by earthquakes. In the roofs of many coal-seams and projecting slightly into the coal are curious conical masses of sandstone, familiar to the miners as “drops.”They are wrinkled on the surface, and often have a flange on two sides, showing that they were produced on the site of a crack. They are ranged in long rows. These are interpreted as casts of the funnel-shaped orifices through which the sands surcharged with water have been expelled. 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. They show contortion where passing through the seam, proving that the coal substance had not undergone its full compression at the time when the fissure was produced. A large number of examples of each type of phenomenon, drawn from the examination of more than thirty mines in the coalfield, are discussed.—Dr. A. Gilligan: Sandstone dykes or rock-riders in the Cumberland coalfield. These sandstone dykes have been encountered in pits distributed all over the coalfield, but those examined were met with in the workings of the Bannock Band and Main Band seams at Ladysmith Pit. The dykes pass through the Bannock Band and Main Band seams and the intervening measures. They run parallel one to the other in a direction N.N.W. and S.S.E. The inclination of the same dyke is not constant, but the greatest deviation from the vertical was 10° south-westwards. The average width of the dykes was from 2 in. to 4 in., but sometimes they increase to 10 in. or dwindle down to mere films. Splitting of the dykes was seen. The contact of the coal and dyke substance was sharply defined, the coal preserving all its normal features even when adhering to the sandstone. The probable conditions which, obtained at the time of the formation of the fissures and their infilling were as follows:—The coal seams through which the dykes pass had been compressed to their present thickness, while they and the associated measures were sufficiently consolidated to take a more or less clean fracture. The sea in which the deltaic material of the Whitehaven sandstone was accumulating covered the area. Fractures were produced by earthquake disturbances set up by movement along one of the N.N.W. and S.S.E. faults, and the sediment on the sea-floor ran in and sealed them up.
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Societies and Academies . Nature 102, 437–440 (1919). https://doi.org/10.1038/102437a0
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DOI: https://doi.org/10.1038/102437a0