C. LAPW0ETH ON THE MOEPAT SERIES. 343 



however, at present buried almost everywhere beneath strata of 

 later age, the lowest visible formation (the Glenkiln Shales) suc- 

 ceeding the volcanic series in point of time, and filling up the 

 interval which is unrepresented in the Lake-district. 



(/) In fine, the facts and inferences detailed in the present paper 

 lead us step by step to the important conclusion that the Lower 

 Silurian rocks of the Southern Uplands are actually arranged in two 

 distinct formations, namely, a lower and very thin group of fine- 

 grained Graptolitic Shales, and an upper and comparatively massive 

 series of arenaceous strata. The latter, though not in reality of 

 extraordinary thickness, is so excessively plicated that it floors more 

 than three fourths of the entire Silurian area, the underlying black 

 shales being visible only at rare intervals along the axes of a few of 

 the more important folds. 



Here, then, for the first time, do we begin to realize the fulfil- 

 ment of the confident prediction of Sir Roderick Murchison, that 

 these apparently interminable Silurian rocks would be found to be, 

 in truth, of reasonable dimensions. The great arenaceous Llandeilo 

 formation of the earlier geologists has utterly vanished, and in its 

 stead wo find a few hundreds of feet of argillaceous shales. The 

 Bala beds are proved to be related to those of the underlying forma- 

 tion in identity of lithological character and in physical conformity, 

 as everywhere in Britain and Western Europe generally, where their 

 natural relations have not been disturbed by an excess of igneous 

 activity. We have, indeed, become unexpectedly aware of the 

 presence of a more than ordinary thickness of Middle Silurian 

 rocks ; but even these may be satisfactorily paralleled with equi- 

 valent strata of corresponding vertical dimensions in the long mis- 

 understood areas of Cardigan and the Thiiringer Wald. 



EXPLANATION OF PLATES XI.-XIIL 



Plate XL 



General maps, showing the geographical distribution of the rocks of the 

 Moffat Series in the typical area of the Moffat District. 



Plate XII. 



Map and sections of the Moffat rocks of the typical locality of Dobb's Linn, 

 Moffatdale. 



Plate XIII. 

 Plans of the chief exposures of tlio Black Shales of the Moffat District. 



