60 DE. T. F. SIBLY OX THE FArLTED INLIEK OF [Feb. I9I2, 



abandoned in 187(3. Large faults encountered at the eastern limit 

 of these workings appear to have determined the cessation of work 

 in this collier}' : these faults have a south-Avesterly trend. Xow, 

 mapping indicates that, at the eastern visible limit of the Upper 

 Vobster iulier, the southern boundary-fault is acquiring a north- 

 easterly trend. These facts lead us to suspect that the southern 

 boundary-fault of the Upper Yobster inlier may be continuous with 

 the above-mentioned faults proved in the Coal Measures on the 

 north-east.^ Should this be the case, the area of Carboniferous 

 Limestone concealed by Lias on the east would be comparatively 

 small. 



The actual junction between the Carboniferous Limestone and 

 the surrounding Coal Measures is nowhere exposed, and I have not 

 succeeded in tracing the boundary between the two formations 

 with much precision. Approximately, however, the proved east- 

 and-west extent of the Carboniferous Limestone is 1100 yards ; 

 and the maximum width of the inlier from north to south is 

 probably little, if at all, greater than 400 yards. 



Vertical Extent. 



Evidence recorded by previous writers appears to prove that the 

 vertical thickness of the Upper Vobster mass of Carboniferous 

 Limestone is small as compared with its horizontal dimensions, and 

 that the whole inlier is practically a thin cake of Carboniferous 

 Limestone and other beds, superimposed upon the strata of the 

 Coal Measures. 



Thus Anstie stated,^ with reference to this inlier, that 



' There is a shaft close to its southern edge from which a level was driven 

 many years ago, completely under the Limestone, to another pit on the north 

 side of it, thus proving it to be a detached block.' 



Anstie did not indicate the precise position of this shaft, but 

 Mr. McMurtrie is undoubtedly referring to the same shaft when 

 he writes ^ : — 



'In the corner of a field adjoining the coal-yard at Bilboa, on the south 

 of the patch [of Carbonit'erous Limestone], are the remains of an old shaft, 

 and I laave been informed upon rehable authority that its workings passed 

 beneath the Limestone. At a depth of eighty yards from the surface a branch 

 or gallery was driven north more than 100 yards, and the men wlio worked in 

 this brancli are said to have been within hearing of the workmen in the Dunny 

 Drift vein at Upper Catch pit situated in tlje northern side of Ihe patch.' 



The position of the shaft in question is shown on a geological 

 map accompanying the paper from which the above is quoted. 

 The site of the shaft, now marked by a mound of shaly debris on 

 which conifers are growing, is indicated on my map (PI. II). 



^ I have to thank Mr. Herbert H. Thomas for this suggestion, and also for 

 kind assistance in consulting the plans of Mells Colliery, deposited in the 

 Home Office. 



2 Anstie, 1873, p. 61. 



3 McMurtrie, 1877, p. 297. 



