478 R. HARKNESS AND H. A. NICHOLSON ON THE STRATA BETWEEN 



high amount of cleavage ; and fossils, though by no means wholly 

 unknown in them, are almost always more or less distorted. At 

 Knock they have yielded only two Graptolites, viz. Monograptus 

 priodon, Bronn, and M. broughtonensis, INich. & Lapw. At Skelgill, 

 and on the high ground between this place and the vale of Trout- 

 beck, they have afforded many specimens of small Brachiopods {Orihis 

 and Discina) and minute Lamellibranchs. These, however, occur 

 only in the form of external and internal casts ; and, as yet, no con- 

 clusion has been arrived at concerning their specific forms. 



The Knock beds are directly surmounted by the well-known 

 and well-marked group the " Coniston Flags," a series of strata 

 corresponding to the "Denbighshire Flags" of North Wales, and 

 which have been clearly shown, more especially by the researches 

 of Prof. Hughes, to be of Upper- Silurian age. As to the exact age 

 of the Knock beds, it is not to be denied that sufficient evidence 

 is yet wanting on which to found any positive or final opinion. 

 They rest upon the Graptolitic Mudstones, which we have shown to 

 be placed nearly or quite at the summit of the Lower Silurian ; and 

 they are overlain by the Coniston Flags, which are quite or nearly 

 the base of the Upper Silurian. It is therefore clear, from their 

 physical position, that the Knock beds must be either the basement 

 series of the Upper Silurian, or the summit series of the Lower 

 Silurian, or a group of passage-beds between these two. 



The palseontologieal evidence at present obtained is not enough to 

 justify us in adopting definitely any one of these hypotheses. So far 

 as it goes, the evidence tends to favour the view which regards them 

 as the base of the Upper Silurians — the only two species of Grapto- 

 lites observed being forms common to the overlying Coniston Flags, 

 whilst there appears to be a complete absence of the genera and 

 species characteristic of the Graptolitic Mudstones. 



Further researches, however, will undoubtedly add to the fauna 

 of this group of beds, and enable its position to be determined with 

 greater precision. 



In the meanwhile it can only be said that the conclusion to which 

 the few known fossils point is corroborated by the strong lithological 

 resemblance between the " Knock beds " and the " Tarannon Slates " 

 of Wales. We cannot, therefore, be far wrong in provisionally 

 regarding the Knock beds as the base of the Upper Silurian series 

 of the Lake- district, in which case the Graptolitic Mudstones will 

 constitute the highest portion of the Lower Silurians of the same 

 area. 



Appendix. — The Irish Representatives of the Coniston Limestone 

 and its associated Rocks. 



Lambay Island and Portraine, co. Dublin. 



On referring to a geological map of the British Isles it will be 

 seen, from the strike of the Coniston Limestone in the southern 

 portion of the Lake -district, and after it disappears under the newer 







