74 THE CAEBONIFEEOUS LIMESTOls'E AT UPPEE VOBSTEE. [Feb. I912, 



blackboard of an inverted anticlinal crest shifted bj- thrust- 

 faulting and stepped by cross-faulting. 



The Atjthoe explained, in reply to Mr. Barro^v, that the 

 quartzites of the Grit-&-Shale Mass were assigned to the Mill- 

 stone Grit, on account of their distinctive lithological character. 

 These beds, seen to a thickness of about 40 feet in the tunnel- 

 section described by Mr. Winwood, were compact pink quartzites. 

 In reply to Mr. Ussher, he stated that the contributions to the 

 literature of Luckington and Yobster, made by that speaker and 

 containing the earliest suggestion of an overthrust, were duly 

 noticed in the paper. He had attempted no discussion of the 

 general tectonic problem of this area to the north of the Mendips, 

 because he thought that the data collected up to the present were 

 inadequate. As to the tectonic theories elalaorated by Mr. H. B. 

 Woodward and Mr. McMurtrie to explain the occurrence of the 

 Luckington and Yobster masses of Carboniferous Limestone, those 

 theories were mentioned in the paper, but not discussed. The 

 extensive overfolding of the Coal Measures in this area was clearly 

 demonstrated by Buckland & Conybeare as early as 1824. 



