DISCOVERY OF SILURIAN" BEDS IN TEESDALE, 



33 



And with this difference in the beds below the Melmerby-Scar 

 Limestone, the differences in the Melmerby Scar-Limestone itself agree. 

 About Brough this limestone is several hundred feet thick, and near 

 the Pencil-mill it would appear to be considerably less ; moreover 

 it is not, in this last locality, at all a pure limestone. It contains, as 

 we have already indicated by the section under the whin at 

 Cronkley, many irregular beds of shale. 



In the sketch map (p. 28) we have only put in these Pencil-mill beds 

 where they are actually to be seen. The great quantity of boulder- 

 clay about would be enough to justify one in this resolution ; but, 

 besides this, we have, of course, to consider the possibility or, rather, 

 probability of changes in the development of the Carboniferous 

 basement-beds. We may state, however, that there is a considerable 

 stretch of flat low-lying land in the corner between Harwood Beck 

 and the Tees, and that these new-found Silurians probably occur 

 over an area out of all proportion to their actual exposure. It 

 would be unnatural to suppose that the whole of this flat area is 

 occupied by beds like those at the Pencil-mill. The Stockdale 

 Shales, which these beds so closely resemble, are usually only several 

 hundred feet thick ; and supposing that these old beds are dipping 

 in Teesdale at any thing like as high an angle as they usually are in 

 the north of England, we should soon get over this thickness and 

 pass on to higher or lower beds. And, indeed, there are positive 

 indications that the whole of this area is not occupied by the Pencil- 

 mill beds. Here and there along the sides of the Tees, in the neigh- 

 bourhood of the Old Mill, loose fragments are found which cannot be 

 referred to any known Carboniferous rock of the neighbourhood, 

 nor to the Pencil-mill bed itself. Some of these pieces appear very 

 like the passage-beds which occur between the Stockdale Shales and 

 the Coniston flags ; they are generally hard dark mudstones with 

 occasional grey gritty bands. There are pieces something like these 

 to be found in the Conglomerate beds which have been described ; 

 and possibly some of them may have been derived thence ; but 

 others are much larger than any thing seen in the Conglomerates, 

 and it is not likely that they have come from them. 



If we exclude this source of supply, there are only two others 

 whence we may suppose them to have been derived. They must 

 either have come from a near spot in Teesdale, and be now not far 

 out of place, or they must have come as drift-boulders over from 

 the west country. Now this last supposition is untenable. It is 

 quite true that thousands of Shap-granite boulders and other west- 

 country rocks have crossed over the Pennine Chain by way of 

 Lunedale Head and Stainmoor ; but the higher Pells just to the north 

 seem to have formed an impassable barrier to the invaders. As 

 far as our present evidence goes, it would seem clear that nothing 

 at all ever came over into High Teesdale by way of Scordale, High 

 Cup Nick, and the higher passes to the north of these. No boulders 

 certainly known to be foreign have been found in the Dale above 

 Middleton ; and the loose pieces in question only occur in the neigh- 



Q.J. G.S. No. 133. d 



