44 'I'rtmmctiuiis. 



hill, and when I say so I simply express the opinion of Pro- 

 fessor Geikie, than whom there is no man more qualified to 

 speak on the question. Confined as the rocks are in a small 

 isolated place, we have everything so condensed, as it were, 

 t'iat nothing but the great characters Avhich distinguish these 

 rocks are brought out in bold relief. The Lake origin of the 

 strata, the great volcanic outbursts of the period, the com- 

 plete absence of any organic remains, and the red colour of 

 the rocks, are all here seen or expressed in the very clearest 

 of geological language. But as it will be utterly impossible 

 to give anything like a comprehensive idea of the develop- 

 ment of all these distinguishing characters in Upper Niths- 

 dale in any paper of moderate length, I propose to draw your 

 attention to-night simply to the origin of the rock basin in 

 which those strata have been deposited. 



(3.) Geological Position and Kelations of these Rocks 

 In pursuing our inquiry, then, it will be necessary, in 

 t'.e first place, to consider the geological position and rela- 

 t uns of the Permian rocks of Thornhill to those underlying 

 and surrounding them. The valley, as I have already said, 

 is a great hollow cut out from the Silurian strata which rise 

 up in the form of hills all round it. Lying along the whole 

 western and southern sides is a stripe of rocks belonging to 

 the Carboniferous Limestone Series. On the eastern side 

 this stripe is more imperfectly developed ; while here and 

 there amongst the Permian rocks these strata also appear. 

 On taking a section of these formations across the valley we 

 find that they occupy the followiug relative position :— (a) 

 We have the Silurian rocks with beds tilted vertically from 

 east to west, across which the valley runs. They rise up on 

 each side as low ranges of hills ; (6) forming the basement 

 beds of this hollow we have the Carboniferous rocks much in 

 the form of a shell, having the central mass of the sandstone 

 cut out, leaving unconnected parts on each side of the valley ; 

 (c) in the hollow thus cut out from the Carboniferous rocks 

 we find the Permian sandstones situated. A section from 



