THE GEOLOGICAL STRUCTURE OF THE CANONB1E COALFIELD. 853 



4. Upper Limestone Group. — The members of this subdivision were proved in an 

 important bore sunk at Rowanburnhead, near the northern margin of the Rowanburn 

 Colliery, to which reference has already been made. A glance at the journal of this bore 

 (see p. 855), and at the diagram of vertical sections, Plate II., shows that the bore was 

 begun in the pavement of the Seven Feet Coal, the position of which in the Rowanburn 

 coalfield is well known. Deducting the thickness of sand and boulder clay at the surface, 

 the first limestone was pierced at a depth of one hundred and eleven fathoms below the 

 pavement of the Seven Feet Seam. Altogether three beds of limestone were passed 

 through, measuring respectively one foot two inches, ten feet, and the lowest, with some 

 intercalations of shale, about twenty feet. Underneath the limestones, as already 

 indicated, lie the thin seams of the Kilnholm coals. 



Further evidence relating to the position of this limestone group was obtained in a 

 bore in the bottom of the Old Furnace Pit, Rowanburn, which showed that they under- 

 lie some thin coals below the Seven Feet Seam. 



Owing to the extensive faulting of the Coal-measures in the Canonbie district, the 

 infraposition of this limestone group to the Lower Coal-measures of Rowanburn has 

 not been proved in any stream section. In the Esk, about one hundred and fifty yards 

 up stream from the foot of Byre Burn, a limestone about three feet thick and calcareous 

 shales appear, charged with Productus, Orthoeeras, and other marine fossils, which may 

 represent one of the bands in this group. 



Upper Carboniferous Rocks. 



Proceeding now to the consideration of the subdivisions of the Upper Carboniferous 

 rocks of Eskdale and Liddisdale, we encounter serious difficulties owing to the absence 

 of any stream sections showing the original order of succession of the various groups. 

 Judging from the evidence visible at the surface, the field-geologist is at a loss to decide 

 the true sequence of the various subdivisions. The area occupied by these rocks in the 

 Canonbie district is so much traversed by important faults, which have obscured the 

 order of superposition, that any attempt to construct a geological map on surface 

 evidence alone would be liable to error. It is not surprising that the Byre Burn Coal 

 group was regarded as lying beneath the Rowanburn coals, nor that the deep bore sunk 

 from the pavement of the Seven Feet Seam was put down with the view of finding the 

 workable coals of Byre Burn below. That attempt proved a failure, though the upper 

 limestones of the underlying Marine Limestone group were passed through in that trial 

 bore. The result of this bore in some measure paved the way for the classification to 

 which Mr Kidston has recently been led by the evidence of the plants, viz., that the 

 Rowanburn coals represent the Lower Coal-measures, the Byre Burn coals the Middle 

 Coal-measures, and the stained red sandstones and shales the Upper Coal-measures. 



