ON STRATA BETWEEN BORROWDALE SERIES AND CONISTON FLAGS. 4G1 



23. On the Strata and their Fossil Contents between the Borrow- 

 dale Series of the North of England and the Coniston Flags. 

 By Robert Harkness, Esq., F.R.S., Professor of Geology in 

 Queen's College, Cork, and H. Alleyne Nicholson, M.D., D.Sc, 

 F.R.S.E., Professor of Natural History in the University of 

 St. Andrews. (Read March 21, 1877.) 



Introduction. 



In the following communication we propose shortly to consider the 

 various groups of strata which intervene between the great volcanic 

 series (Borrowdale Rocks) of the Lake-district and the well-marked 

 band of sedimentary rocks to which Prof. Sedgwick applied the 

 name of the " Coniston Flags." In so doing we shall have occasion 

 to note, in a general way, the physical characters and relations of 

 the successive deposits in question ; but we shall have to draw 

 attention more especially to the organic remains which they con- 

 tain and to some indications thus afforded as to their precise age 

 and position in the geological scale. 



The base of the great Silurian series of the north of England is 

 constituted, as is well known, by the " Skiddaw Slates," a thick 

 mass of sediments, originally in the condition of black mud, clearly 

 proved by their fossil contents to be of the age of the "Arenig 

 group " of Wales. Succeeding the Skiddaw Slates there occurs a 

 great series of volcanic products, termed by Prof. Sedgwick the 

 " green slates and porphyries," to which we have elsewhere given 

 the name of " the Borrowdale series." These consist of ashes and 

 breccias, alternating with ancient lavas, a portion of the series being 

 subaerial, whilst part is of submarine formation. 



Throughout the greater part of this extent, for a thickness of 

 some thousand feet, the Borrowdale series has hitherto proved un- 

 fossiliferous ; fossils, however, make their appearance in a thin 

 band of calcareous ashes near the summit of the group (Harkness 

 and Nicholson, Quart. Journ. Geol. Soc. vol. xxii. p. 480). 



In some places, as at Style-End Grassing, between Long Sleddale 

 and Kentmere, this band consists of brownish or bluish grey shales, 

 and it is separated from the Coniston Limestone by a bed of trap. In 

 other spots, as at Sunny Brow, between Ambleside and Coniston, the 

 bed is siliceous and gritty in nature. At Millom the same fossiliferous 

 band is recognizable, and is not only ashy in its character, but is 

 surmounted directly by strata belonging to the Coniston Limestone 

 series without the intervention of traps. Lastly, there are places, 

 such as the east side of Long Sleddale and the southern declivity of 

 Wansfell, where the same beds can be readily recognized, having 

 the same relation to Coniston Limestone, similar to the ordinary 

 ashes of the Borrowdale series in their ordinary character, and ex- 

 hibiting no traces of fossils beyond the presence of innumera- 



