476 R. BARENESS AND H. A. NICHOLSON ON THE STRATA BETWEEN 



If it be remembered that along one line of ontcrop alone, from 

 Appletreeworth Beck to Shap Wells, the Graptolitic Mudstones can 

 be traced almost continuously succeeding the limestone for a distance 

 of about twenty-four miles, it will be seen to be almost impossible 

 that any want of conformity, however slight, could exist without 

 there being, at the same time, a transgression of the Mudstones over 

 the Limestones. It is true that, owing to the circumstance that the 

 calcareous matter of the Coniston Limestone series is disposed in the 

 form of irregular lenticular masses or concretionary layers, the litho- 

 logical character of the bed immediately below the Mudstones is not 

 invariably the same, being at one time a limestone and at another 

 a calcareous shale. This, however, is due to an irregularity of de- 

 position which obtains throughout the entire limestone series ; and 

 we have failed to find any evidence that the Graptolitic Mudstones 

 ever rest upon any of the lower beds of the Coniston Limestone. 

 As the latter group is of small thickness, and as its main line of 

 outcrop is a very long one, such an overlap must occur, supposing 

 unconformity to exist ; and in all probability we should even find 

 the Mudstones passing across the limestones and resting upon the 

 older Borrowdale series. 



The absence therefore of any unobserved overlap is, under the 

 circumstances, the strongest possible proof that the Mudstones are 

 entirely conformable to the Coniston Limestone. 



That the Graptolitic Mudstones constitute a geological horizon of 

 a definite character, and of much more than mere local importance, 

 is shown by the fact that they can be recognized in Ireland in cir- 

 cumstances similar to those under which they occur in the north- 

 west of England (see Appendix). They have also been recognized 

 in Sweden, in Carinthia, and in Bohemia, while future researches 

 will doubtless bring corresponding strata to light in other Lower- 

 Silurian regions. 



In Sweden Dr. Linnarsson has shown (Geol. Mag. June, 1876) 

 that the so-called " Upper Graptolitic Schists " are the equivalents in 

 that countiw of the Graptolitic Mudstones of the north of England. 

 These Upper Graptolitic Schists, as seen in Westrogothia and Ostro- 

 gothia, are the highest Silurian rocks exposed to view, so that they 

 add nothing to the evidence as to the age of the Coniston Mud- 

 stones. 



In Scania, however, they are overlain by undoubted Upper Silurian 

 beds ; and in Dalecarlia they are surmounted by a locally developed 

 limestone (the " Leptsena Limestone " of Tornquist), which appears 

 to form either the summit of the Lower Silurian or the base of the 

 Upper Silurian, being in turn covered by the undoubted Upper 

 Silurian "Encrinu rws-beds." Upon the whole, therefore, the evidence 

 to be derived from the Swedish area entirely corroborates the view 

 that the Graptolitic Mudstones are of Lower-Silurian age. 



In Carinthia, beds corresponding precisely with the Graptolitic 

 Mudstones have been described by Dr. Guido Stache (Die Grapto- 

 lithen-Schiefer am Osternig-Berge in Karnten) ; and the parallelism 

 of the two deposits has been fully noticed by this distinguished 



