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



Discinocaris, are found in the darkest and most highly fossiliferous 

 graptolitic zones. The Trilobites were obtained exclusively from a 

 dark grey band lying between two graptolitiferous bands, about ten 

 feet above the highest bed of the Coniston Limestone. 



Lastly, all the Brachiopods, with the exception of a common but 

 undetermined Orthis of small size, were procured from a single band, 

 the position of which is shown with absolute clearness at several 

 points in the course of Skelgill Beck. 



The highest bed of the Coniston Limestone in this locality is for- 

 tunately actually a limestone, and not merely a calcareous shale ; 

 and it is seen at various points to be directly overlain by a thin 

 band of the characteristic black Mudstone, not more than six or 

 eight inches in thickness, containing numerous Graptolites (Clima- 

 cograptus &c). The direct contact and juncture of the limestone 

 and the above-mentioned graptolitiferous band can be observed at 

 various spots ; and the latter is at once surmounted by a dark grey 

 shale, about eighteen inches in thickness, from wiiich Graptolites 

 are almost entirely absent, but in which the great majority of the 

 Brachiopods were obtained ; and this shale is immediately succeeded by 

 a second graptoliferous band. The shale affording the Brachiopods is 

 highly cleaved ; and these shells are, unfortunately, so much distorted 

 as to render their determination a matter of considerable difficulty. 

 The Trilobites, on the other hand, occur in a zone several feet higher 

 in the series, surmounted in turn by other graptolitiferous beds, and 

 they are so well preserved as to admit of ready and complete iden- 

 tification. 



Any doubt which might have been previously entertained as to 

 the precise age of the Graptolitic Mudstones seems to be removed 

 by the fossils recently obtained from these beds. 



It has been already mentioned that these Mudstones were to be 

 regarded as of Lower- Silurian age; and the materials at present in 

 our hands appear entirely to confirm this view. Leaving the evidence 

 afforded by the Graptolites to be considered separately, it is impos- 

 sible to doubt that the fauna of the Mudstones is essentially a Lower- 

 Silurian fauna. Amongst the Trilobites Agnostus trinodus, Phacops 

 apiculatus, Calymene senaria, Trinucleus jimbriatus, and Cheirurus 

 bimucronatus are characteristic Bala forms ; and all of them, with 

 the exception of the last mentioned, are exclusively confined to 

 rocks of Lower- Silurian age. . Harpes Flanagani, the sole remaining 

 form that we have been able to determine with certainty, is a Bala 

 type from Tyrone and Desertecreat. The Discinocaris is closely 

 allied to if not absolutely identical with D. Brouniana, a well-known 

 fossil from the graptolitic Lower Silurians near Moffat. 



Of the Cephalopoda the singular Endoceras proteiforme is a cha- 

 racteristic fossil of the Trenton Limestone (Llandeilo-Caradoc) of 

 North America, and Orthoceras angulatum ranges from the Bala to 

 the Ludlow group. The Brachiopoda, even when so much distorted 

 as to be specifically indeterminable, have nevertheless a distinct 

 Lower- Silurian facies ; and Orthis vespertilio with Strophomrna 

 expansa are characteristic types of the Bala rocks. Lastly, the few 







