THE B3RR0WDALE SERIES AND THE C0NIST0N FLAGS. 477 



observer. Unfortunately the succession of the Silurian strata in 

 the Osternig is still so obscure as not to permit of any safe con- 

 clusions being drawn as to the precise stratigraphical horizon of 

 these beds, though Dr. Stache concludes that they stand on the 

 borderland between the Lower and Upper Silurians. 



In Bohemia we find the representatives of the Graptolitic Mud- 

 stones in the "Colonies" of Barrande's Etage D and in the lower 

 portion of the Etage E of the same eminent palaeontologist. 



These beds, as is well known, are referred by M. Barrande to the 

 base of the Upper Silurian. 



Without, however, entering fully into this question here, and dis- 

 regarding the strong evidence which we now hold as to the Lower- 

 Silurian age of our Graptolitic Mudstones, we would simply point 

 out that M. Barrande himself fully admits that the succession of 

 Silurian life in the Bohemian area was later, stage by stage, than in 

 the northern European and British areas. Thus he supposed that 

 the Bohemian area was peopled with a general Loiuer-^bxumn. fauna 

 at a time when the North European and British areas were peopled 

 with a general Upper-$ibxrian fauna, and he employs this suppo- 

 sition to explain the phenomena of the " Colonies." Admitting 

 therefore that the " Colonies " and the lower portion of Etage E are 

 Upper Silurian, it would in no way follow that the corresponding 

 Graptolitic Mudstones of the north of England are also Upper 

 Silurian. On the contrary, by M. Barrande's own theory, the 

 Graptolitic Mudstones ought to be Lower Silurian, being thus " ho- 

 motaxeous," but not " contemporaneous " with the lower part of 

 Etage E of Bohemia. We thus see that the evidence to be derived 

 from Bohemia, though apparently at conflict with our views as to 

 the age of the Graptolitic Mudstones, is, when fully analyzed, an 

 additional argument in favour of our conclusions. 



4. Knock Beds. 



The Graptolitic Mudstones are succeeded by a series of strata for 

 which the name of "Knock beds" has been proposed (Nicholson & 

 Lapworth, Rep. Brit. Assoc. Bristol, 1875), on account of their ex- 

 cellent development in Swindale Beck, near Knock. Lithologically 

 the Knock beds present a singular uniformity wherever they are 

 found, enabling them to be recognized with the greatest readiness. 

 They consist principally of pale green, fine-grained slates, extremely 

 ashy in their appearance, exhibiting numerous dendrites, and very 

 commonly containing crystals of cubic pyrites. Along with these 

 greenish slates are often well-marked bands of red and purple slates 

 of the same grain and texture as the preceding; and occasionally 

 there is met with a thin band having a grey or even a nearly black 

 colour, though this is exceptional. The general strike and dip of 

 the Knock beds conform with those of the underlying Graptolitic 

 Mudstones ; and there is, at present, no clear evidence of any want 

 of conformity between the two groups. 



The Knock beds have been subjected to a varying but always a 



