470 K. HARKNESS AND H. A. NICHOLSON ON THE STRATA BETWEEN 



(3) The presence, near the summit of the Coniston Limestone 

 itself, at Shap Wells, of a calcareous breccia containing numerous 

 fragments of ash proves that an eruption took place towards the 

 close of the period during which the Coniston Limestone was depo- 

 sited. Nor does the site of this eruption appear to have been very 

 far removed from Shap Wells itself ; for the microscopic investiga- 

 tion of this breccia indicates that some of the older and previously 

 formed beds of the Coniston Limestones were broken up by this 

 outburst, and were thrown over the sea-bottom along w r ith innu- 

 merable fragments of ash, the whole being subsequently cemented 

 together by calcareous ooze to constitute the singular stratum in 

 question. 



(4) The presence in the Coniston Limestone in the Sedbergh 

 district, as shown by Prof. Hughes, of interbedded felstones, proves 

 conclusively the occurrence of volcanic eruptions contemporaneous 

 with the deposition of the limestone, in this area at any rate, if not 

 elsewhere. 



(5) By the supposition we have brought forward a satisfactory 

 explanation is obtained of a certain amount of apparent discordance 

 between the Coniston Limestone and the underlying volcanic Bor- 

 rowdale rocks. This discordance, so far as it exists, might be set 

 down as due to a want of conformity ; but we do not think that this 

 is its true explanation. 



If the views we entertain be correct, it is rather due to the fact 

 that the Coniston Limestone was deposited round the shores of the 

 volcanic nucleus of the Lake-district very much after the fashion 

 that a modern limestone might have been in process of formation 

 for thousands of years off the coasts of Sicily. In such a case beds 

 of limestone would wrap round sheets of lava so as to be apparently 

 transgressive thereon, or might be interstratified with strata of tuff, 

 of ash, or of volcanic rocks. Any seeming discordance between the 

 calcareous series and the volcanic products would be due, not to 

 absolute unconformability, indicating a lapse of time, but simply to 

 the difference in the method by which the two groups were 

 formed. In spite of any apparent discordance, both groups would 

 belong to the same period, and in part they w^ould be actually con- 

 temporaneous. 



If these inferences be confirmed by further researches, it will 

 follow that the Borrowdale rocks must be regarded as being of 

 Lower-Bala age. As the Skiddaw slates are unquestionably Arenig, 

 and the Coniston Limestone equally unquestionably Bala, the only 

 other view which could be taken as to the Borrowdale series would 

 be to refer them to the Llandeilo. Apart, however, from the con- 

 siderations just mentioned, this view is rendered unlikely by the fact 

 that the great series of Llandeilo rocks developed in the south of 

 Scotland appears to be wholly free from intermixture with con- 

 temporaneous igneous matter. "We can hardly suppose that such 

 could possibly have been the case, if the Llandeilo strata of the 

 southern uplands of Scotland had been in process of formation at a 

 time when the closely adjoining region of the Lake-district was the 



