160 



MESSRS. KIRKBY AND DUFF ON THE 



Quarter are subject to considerable variation in the nature of 

 their roofs. Most generally the stratum overlying the coal is 

 argillaceous, in the form of shale (or "metal"), which is occa- 

 sionally of great thickness. At other times it is sandstone, either 

 with a thin layer of shale between it and the coal, or resting 

 directly on the latter itself. In this case it is often curious to 

 observe the evenness and regularity with which the sandstone 

 appears to have been deposited on the coal over very extensive 

 areas, when we consider that the laying down of the materials 

 of such rocks is generally accompanied by powerful and rather 

 erratic current action. But as a rule it is only rarely that traces 

 of such action are evident. One of the most interesting of these 

 occurred to us in the Five Quarter coal at Lands Pit, where a 

 sandstone, lying about five feet above, descends abruptly through 

 the shale roof and for three feet into the coal, as shown in the 

 following sectional view, fig. 2, in which A is a yellow sand- 

 stone ; B lightish grey shale, with fossil plants, about five feet 

 thick ; C coal five feet three inches thick ; D fireclay. The 



"Stone Roll" iu Five Quarter Coal, Lands Colliery. 



sandstone in other parts of Lands Pit forms the roof of the coal, 

 but it is here superimposed on from three to five feet of shale, 

 its line of junction with the latter being very irregular, as though 

 the shale had been partially denuded before the deposition of the 

 sandstone. Indeed there can be little doubt of this being the 

 case, and of the " stone roll" figured representing a part more 

 deeply denuded than usual. We were unable to trace its course 

 far, though it was observed in other adjacent bords. Its width 

 was about five yards at the top of the coal. 



