THE BORROWDALE SERIES AND THE CONISTON ELAGS. 469 



regarded as unquestionably of Bala age. This is shown conclusively 

 by the Brachiopods, and especially by Trilobites of the following 

 forms — Sphcerexochus mirus, Cheirurus juvenis, C. cancrurus, C. 

 gelasinosus, C. octolobatus, Lichas laxatus, L. hibernicus, Illcenus 

 Bowmanni, I. Davisii, Phacojps macrourus, P. apiculatus, constituting 

 amongst the latter a characteristic assemblage of Caradoc or Bala 

 types. It is somewhat curious that of the two commonest and most 

 characteristic Trilobites of the Dufton shales, Galymene Blumen- 

 bachii is hardly known in the Coniston Limestone, and Trinucleus 

 concent ricus is generally absent. The latter occurs plentifully in the 

 " Trinucleus- shales " of Prof. Hughes, a locally developed group at 

 the summit of the Coniston Limestone in the Sedbergh district. 

 The evidence to be derived from the Brachiopods is equally con- 

 clusive with that of the Trilobites, all the common forms being cha- 

 racteristic species of the Bala formation ; but it is not necessary to 

 enter into further details on this point. 



It remains briefly to consider the conditions under which the 

 Coniston Limestone series was deposited. On this matter we wish 

 especially to indicate that there seems to be good evidence that the 

 volcanic activity which produced the vast mass of ash, breccias, and 

 lavas constituting the Borrowdale series, though greatly mitigated 

 in intensity, had not entirely died out during the period of the 

 deposition of the Coniston Limestone and Dufton Shales, but con- 

 tinued to operate at occasional intervals. It would seem probable 

 that the Lake-district was not entirely submerged at the time when 

 the Coniston series began to be laid down, but that a portion of 

 the volcanic region remained above the level of the sea, its vents 

 occasionally giving exit to showers of volcanic ashes or even currents 

 of lava. If this hypothesis be established, it would follow that there 

 was no breach of continuity between the close of the Borrowdale 

 series and the commencement of the Coniston series, but that the 

 two groups of rocks are intimately related, and in point of fact 

 actually overlap one another in time. The principal grounds which 

 at present appear to indicate the correctness of this hypothesis may 

 be briefly stated as follows : — 



(1) The intercalation in the Borrowdale series, close to its summit, 

 of a band of fossiliferous shales containing Bala species, proves that 

 the volcanic energy of this period still continued in force at a time 

 when the sea was peopled with well-known Bala Brachiopods and 

 Trilobites. The shales in question (Style-End Grassing beds) are 

 usually separated from the Coniston Limestone proper by a mass of 

 lava ; but they are undoubtedly to be regarded as, palseontologically, 

 a portion of the Coniston series. 



(2) The presence of beds of ashes, containing numerous fossils, 

 high up in the Dufton Shales at Swindale, near Knock, proves simi- 

 larly that the volcanic eruptions of the preceding period had not 

 entirely ceased at the time when the Dufton shales were in course 

 of formation, and these shales, as we have seen, belong palaeonto- 

 logically to the Lower Coniston group, and are only a local develop- 

 ment of the base of the Coniston Limestone itself. 



