J. E. MARR ON LIFE-ZONES OE THE SILURIAN. 871 



50. On some well-defined Life-zones in the Lower Part of the Silu- 

 rian {Sedgwick) of the Lake-district. By J. E. Marr, Esq., 

 Scholar of St. John's College, Cambridge. (Bead June 19, 



1878.) 



[Communicated by Prof. T. M c Kenny Hughes, M.A., F.G.S.] 



The following paper treats of the different zones of fossils occurring 

 in the strata between the Coniston Limestone and the Coniston 

 Grits of the Lake -district, with the view of correlating the beds in 

 the more central part of the district with those of the outlying dis- 

 tricts in the neighbourhood of the Pennine chain, and of establishing 

 the position of the boundary between the Cambrian and Silurian 

 formations. This boundary, as indicated by the palaeontological 

 evidence, coincides with the position already assigned to it by Prof. 

 Hughes, from the study of the district east of the river Lune (Geol. 

 Mag. vol. iv. no. 8). 



A marked feature in the fauna of the Lake-district beds of these 

 formations is the frequent occurrence of the genus Phacops at dif- 

 ferent horizons, each fossiliferous formation being characterized by 

 one or more species of its different subgenera, as seen in the fol- 

 lowing list : — 



Formation. Characteristic Phacops. 



Kirkby-Moor Flags . . . Phacops ( Odontochile) caudatus, var. minor, and Ph. 



(Acaste) Bowningia. 



Bannisdale Slates Phacops (Acaste) BowningicB. 



Coniston Grits Phacops (Acaste) Bowningice. 



Coniston Flags Phacops ( Odontochile) obtusicaudatus. 



Stockdale Shales Phacops (proper), sp. 



Ashgill Shales Phacops ^(Odontochile) mucronatus, var., and Ph. 



(Acaste) apiculatus. 

 Coniston Limestone .. . Phacops (Chasmops) macroura, and Ph. (Chasmops) 



conophthalmus. 



Green Slates (No fossils.) 



Skiddaw Slates Phacops (Acaste) Nicholsoni. 



The zones marked by these species of Phacops will be found to 

 hold good when the organic remains as a whole are considered. 



Beginning at the lower beds, the Skiddaw Slates and Green Slates 

 have already been fully treated of by many geologists, notably by 

 Profs. Harkness and Nicholson, and the Coniston Limestone has also 

 been admirably described by the same authors ; but a series of beds 

 has been included in this formation, which I hope to show, both on 

 palaeontological and stratigraphical grounds, should be cut off from 

 it as a distinct subdivision. If these beds be so dealt with, it will 

 cause some little modification in all the lists of the Coniston-Limestone 

 fossils hitherto published, except that given by Prof. Hughes in the 

 above-mentioned paper, in which the two formations are locally 

 distinguished and separate fossil lists given. 



