[ «6 ] 



L. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 426.] 



January 8th, 1919.— Mr. G. W. Lamplugh, F.R.S., President,. 

 in the Chair. 



r PHE following communications were read : — 



1. ' On " Wash-outs " in Coal- Seams and the Effects of Con- 

 temporary Earthquakes.' By Percy Fry Kendall, M.Sc, F.G.S., 

 Professor of Geology in the University of Leeds. 



The author differentiates two types of interruptions in coal- 

 seams which have been confused under the general term of 

 'wash-outs,' 'wants,' 'nips,' or ' dumb -faults.' One type he 

 believes to be due, as geological writers have mostly held, to 

 erosion by contemporary or sub-contemporary streams which 

 coursed through the alluvial area where the coal-material wa& 

 accumulating as a species of peat. The channel thus cut was. 

 subsequently infilled with sedimentary materials. 



He describes a number of examples of this type in the Midland 

 Coalfield, some being sinuous in course and traceable over many 

 miles; others being of great width and of irregular form, and 

 due possibly to shifting and meandering streams. 



Split seams of the type in which the seam rejoins are kindred 

 phenomena, but in these cases the erosion was always con- 

 temporary, and, after a channel was filled up with sediments, 

 peat-producing plants spread completely across the infilling. 



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, coal undergoing a- 

 shrinkage variously estimated from f- - to ■JJ- of the peat from 

 which it is formed; mud undergoing, as Sorby showed, a con- 

 siderable though lesser degree of reduction ; and sand undergoing 

 almost no reduction at all. Thus the hog-back section of split 

 seams is due to the shrinkage of the enclosing coal-substance 

 letting down a relatively -incompressible infilling of a channel 

 deeper in the middle than at the sides. In the process the lower 

 surface of the sedimentary mass would flatten to adjust itself to 

 the floor, and the top would consequently assume a curve corre- 

 sponding generally with the original lower curve, but reversed. 

 The upper element of the seam has some species of seat-earth 

 which arches over the hog-backed inclusion. 



Cannel, which the author considers to be due to a kind of 

 vegetable pulp that underwent most of its decomposition and 

 chemical change coincidentally w r ith deposition, acts as a substance 

 of little compressibility ; and, whenever pools of cannel-pulp took 



