Vol. 58. | DISTURBANCES IN BRAYSDOWN COLLIERY. 617 
that the variation in amount of overthrust in the faults appears to 
cease below the Bull Vein: the first seam of the Farrington 
Series having the same amount of overthrust as the last in the 
Radstock Series. Therefore, as there has been comparatively little 
variation in the relative amount of movement in this series, there 
has consequently been little friction between the beds, and as a result 
little dead ground, and little thinning of the seams; while, in con- 
trast with this, the Lower Ccal-Measures of the Nettlebridge Valley, 
which have been considerably crumpied and distorted, contain 
much dead ground. 
DISscUSSION. 
The Prestpent expressed his appreciation of the careful observa- 
tion of facts and cautious inference from them, evinced by the 
Author of this paper, which afforded fresh evidence in support of 
the opinion that it is in the study of minor and local phenomena 
that we may eventually find the clues to the interpretation of the 
grander deformations which affect vast tracts of country. He had 
himself often urged that in all likelihood the majority of the under- 
ground abnormalities in British coal-seams generally, such as the 
so-called ‘ wash-outs,’ ‘horsebacks,’ etc., the local thickenings and 
thinnings, and the occasional temporary disappearance of coal- 
seams, might be due merely to subsequent deformation ; but few 
mining men were as yet willing to concede this. It was to be hoped 
that the publication of the Author’s results would prompt others who 
had met with corresponding phenomena in coal-workings to bring 
forward similar papers, and place the facts on record for the benefit 
both of geology and of economics. 
Prof. Bory Dawxins welcomed the paper, and fully accepted the 
conclusion that the phenomena described are the result of over- 
thrust-faulting in this district, which is traversed by the Axis of 
Artois of Godwin-Austen. Along a line reaching from the South 
of Ireland on the west, to the Boulonnais and beyond on the east, 
similar overthrusting is conspicuous. In the Boulonnais it is illus- 
trated by the fact that in one section the Devonian rocks have been 
thrust over the Coal-Measures, in which three seams of coal have 
been won, by shafts through the above rocks. In the whole of this 
region the absence of seams of coal from their natural position 
was mainly, if not entirely, due to overthrust. In other regions, 
however, as in the Forest of Dean and the South Yorkshire Coalfield, 
the absence of coal-seams was due to the cause usually assigned— 
the action of water traversing the Carboniferous morasses (now 
coal-seams), and depositing sand and mud, now sandstone and 
shale, in these old channels. 
Prof. Groom said that facts gleaned from the adjacent area of 
the Forest of Dean seemed to lend support to the Author’s con- 
tention that the so-called ‘ wash-outs’ in Somerset were due to 
dislocations. Mapping on the eastern side of the Dean-Forest Coalfield 
