Rev. J. Clifton Ward — Geology of the Lake District. 121 



First, I would remark that this name — indicating the supposed 

 age and the equivalent in Wales — has been given to the whole 

 thickness of some 10,000 feet. Second, that this opinion is founded 

 almost entirely upon the presence of certain groups of Graptolites. 

 Third, that Graptolites are notably capricious in their distribution — 

 witness in the Lower Silurians of Scotland the immense thickness of 

 non-graptolite bearing and unfossiliferous strata associated with the 

 one or two black shale bands bearing Graptolites. Fourth, that in 

 the Skiddaw Slate Series as a whole there are several alternations of 

 deposits varying much in character — an upper black slate series, a 

 marked grit or gritty series, again a black and irony series of slates, 

 passing down into a great thickness of sandy and gritty beds. 

 Fifth, that the majority of the Graptolites have been found in beds 

 above the upper grit, but that they also occur in those below the grit, 

 where the sediment seems to have been favourable for their existence ; 

 while there are a few cases apparently of their occurrence even 

 among some of the flaggy beds of the lower sandy and gritty series. 

 With these preliminary remarks, I will pass, first, to the consider- 

 ation of physical evidence as to subdivisions and their possible 

 equivalency to Welsh Lower Silurians. 



Points of Physical Evidence. — I had been working for some years 

 upon the Lake District rocks, when Prof. Eamsay called me into 

 Wales to trace a base to the Arenig series marked by a thin grit. 

 In carrying out this work, I was often struck by the general resem- 

 blance in sequence of the deposits both above and below the grit to 

 that of a like series in Cumbria, and on returning to the Lake 

 country examined more closely the characteristics of the various 

 parts of the Skiddaw Slates. The resemblance in physical character 

 between the Arenig grit of Wales and the upper grit of the Skiddaw 

 Series is perfect. With one or two local exceptions, the Cumbrian 

 upper grit is thicker than the Welsh Arenig, but both are made up 

 of similar materials, both vary much in coarseness, though almost 

 always presenting some coarse gritty or conglomeratic portion, and 

 both are much traversed by quartz strings. The constancy of the 

 Arenig grit in N. Wales, though often not exceeding 12 or 20 feet, 

 is surprising, and the fact is at any rate worth recording that among 

 strata of somewhat parallel age in Cumbria there occurs a like grit. 

 Moreover, in Wales the Arenig slates above the grit soon become 

 mixed with volcanic deposits, submarine volcanic ejecta, and in 

 Cumberland we have in the northern or Skiddaw district a consider- 

 able thickness of black Graptolite-bearing slates succeeded by a 

 Volcanic Series, and in the south-western part, at Lank Rigg and 

 Latterbarrow, the same Volcanic Series lying directly upon the grit. 

 (See also previous remarks on this subject, page 51.) 



Turning to the beds below the grit, we have in Wales the iron- 

 stained Tremadoc Slates underlaid by a great thickness of flaggy, 

 sandy, and gritty beds, the Lingula Flags. In Cumbria there is a 

 like physical sequence; beneath the grit come black iron-stained 

 slates, often quite indistinguishable from the Tremaclocs of North 

 Wales, underlaid by a great but unknown thickness of flaggy, sandy, 



