Vol. 62.] AN T7NCONFOKMITY IN THE COAL-MEASUEES. 551 



Mr. J. T. Stobbs said that the North-of-England Institute of 

 Mining & Mechanical Engineers had published a very valuable and 

 unique set of sections of borings and sinkings in connexion with 

 the great Northern Coalfield, for which he believed they were largely 

 indebted to Prof. Lebour. In these volumes the sections of shafts at 

 Whitley, Hartley, ChoppiDgton, and West Cramlington record the 

 ' mussel-bands' above the Low-Main Seam, showing that this uncon- 

 formity had not cut deeper than these bands over a very considerable 

 area. He would like to ask Prof. Lebour whether these facts would 

 not prove helpful in estimating the magnitude of the unconformity. 



Mr. Philip Lake said that he was fully prepared to accept the 

 Authors' interpretation, and asked whether the unconformity was 

 accompanied by any palaeontological change which might help to 

 determine its magnitude. 



Prof. Lebot/k, in reply, said that it was gratifying to him and his 

 fellow-Author to find that so many had taken part in discussing 

 what, they were afraid, might have been regarded as a dry paper on 

 a merely local question. He would not be surprised if it turned 

 out in the end that every criticism that had been offered was 

 correct — more or less. He did not know for certain whether the 

 eoal-seam beneath the plane of disturbance was in truth the Low- 

 Main Seam : it probably was. He had had doubts as to both the 

 unconformity and the thrust, but the evidence detailed in the paper 

 had tended very largely to dispel such doubts. It was probable 

 that even now what he did not know, respecting all the points 

 involved, was considerably more than what he did know. As to 

 the many volumes of North-Country borings and sections referred 

 to by Mr. Stobbs, he could not help knowing them, since he had 

 helped to edit them from the beginning. He knew of no difference 

 between the fossils in the beds above or below the unconformity. 

 The important suggestion made by Mr. Lamplugh was one which 

 had forced itself upon the attention of the Authors long ago ; but 

 some of the pebbles were manifestly waterworn, and their long 

 exposure to weathering (in the case of the rolled fragments of 

 mussel-band) seemed to the Authors sufficiently attested by the 

 chemical arguments brought forward in the paper. If Mr. Lamplugh 

 could arrange to visit the section, the Authors would gladly abide 

 by his verdict. 



Q. J. G. S. No. 248. 



