Yol, 68.] CAEBONIFEROtlS LIMESTOXE AT UPPER TOBSTEPv. 59 



faults to explain the phenomena. Mr. McMiirtrie, strongly com- 

 bating this explanation, has elaborated an ' overthrow theory ' in 

 its place. The latter writer has given descriptive notes on each 

 of the three inliers, and recorded many important facts in regard 

 to them. 



Two papers ^ by the Eev. H. H. Win wood, which give the details 

 of a quarry- section and a tunnel-section exposed in the Upper 

 Yobster mass in 1882, are especially valuable, because the tunnel- 

 section, now almost entirely concealed, gives the key to the structure 

 of this inlier. Further reference will be made to these and other 

 papers. 



The present paper is limited to a description of the Upper Yobster 

 mass. This inlier, intermediate in position, is not only by far the 

 largest of the three, but also the only one in which any satisfactory 

 exposures are at present available. 



AYith reference to the wider subject of the large tectonic features 

 to which these masses of Carboniferous Limestone owe their present 

 position, no discussion is offered here. We may conclude with 

 tolerable certainty, as will be shown in the sequel, that the 

 occurrence of these inliers is due to thrust-faulting'^ 

 connected with the proved overfolding of the Coal 

 Measures; but a proper discussion of the structural problem must 

 await the re-survey of the whole district. 



My thanks are due to Mr. J. W. Tutcher and Prof. 8. H. Eeynolds 

 for their kindness in furnishing the photographs (reproduced in 

 Pis. III-Y) which illustrate this paper. 



II. Extent of the Inlier. [Map & Section, PL IL] 



Horizontal Extent. 



The rocks forming the Upper Yobster inlier consist mainly, but 

 not entirely, of Carboniferous Limestone. On the south and west 

 their outcrop is bounded by that of the surrounding Coal Measures : 

 on the north and east, however, the outcrop of the Carboniferous 

 Limestone is cut off by the Lias, and a considerable portion of the 

 inlier may be concealed by the thin covering of this latter formation. 

 The position of various small mounds of shaly debris which mark 

 the sites of trials for coal, indicates that on the north, beneath the 

 Lias, the Carboniferous Limestone is soon cut off by Coal Measures ; 

 but no such evidence is available to indicate the limit of the inlier 

 beneath the Lias on the east. 



With reference to the question of the eastern limit of the inlier 

 the following facts are, however, worthy of consideration. Less 

 than half a mile north-east of the exposed portion of the Upper 

 Yobster inlier are situated the old workings of Mells Colliery, 



1 AVinwood, 1885, 1893. 



- This explanation was suggested, many years ago, by Mr. W. A. E. Ussher. 

 SeeUssher, 1889, 1891. 



