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with them may be Hght- or dark-brown, light- or dark slate -coloured, 

 or black. These colours thus contrast decidedly with the wholly 

 or mainly red tints of the overlying Permian and Triassic (or 

 Poikilitic) sandstones and shales. But exceptions occur. In the 

 Yorkshire Coalfield a massive sandstone, known as the "Red Rock 

 of Rotherham," and some other rocks towards the Permian, or 

 eastern, boundary of the coalfield, are so much redder in tint than 

 is usual in Carboniferous beds, that they were formerly classed 

 with the overlying Permians. But the evidence collected during 

 the Geological Survey of the Yorkshire Coalfield showed that the 

 Red Rock, though it lies unconformably on the Carboniferous 

 rocks below, is also unconformable to the Permian Rocks above. 

 For in a railway cutting a little S.W. of Rotherham, Coal Measure 

 rocks of ordinary appearance are seen overlying the Red Rock. 



A very similar state of things is found in Cumberland, where 

 the "Whitehaven Sandstone" takes the place occupied by the 

 Red Rock of Rotherham in Yorkshire. And, like the Red Rock, 

 the Whitehaven Sandstone was, till quite lately, considered to be 

 either Permian or Triassic, instead of Carboniferous. For at 

 Whitehaven, where it is best shown, it rests unconformably on 

 Coal Measures of ordinary hue, and differs from them in its redder 

 tint. But the classification of the Carboniferous Whitehaven 

 Sandstone as Permian or Triassic has led to errors of more 

 importance than the Red Rock has occasioned in Yorkshire. 

 For, near Rotherham, the Red Rock and the other reddish beds 

 invariably belong to the upper part of the Coal Measures, and no 

 important practical error could arise from supposing them to be 

 Permian. But in Cumberland the red or reddish Carboniferous 

 rocks are of very various ages ; from Upper Coal Measure (for 

 instance) about Bullgill and elsewhere in the west, to Millstone 

 Grit or Yoredale age in the Caldew on the east. In both counties 

 there are both conformable and unconformable red-stained Car- 

 boniferous rocks. But the unconformity between the Carboniferou s 

 and Permian formations is much greater in the district, for example* 

 south of Wigton, than in that east of Rotherham. Two simple 

 diagrams will illustrate better than many words could do, the 



