THE BORROWDALE SERIES AND THE CONISTON FLAGS. 



465 



hard grey or bluish grey, cleaved, and often highly calcareous 

 shales, containing numerous nodules or thin but distinct bands of 

 limestone. In some places the beds of limestone are the most 

 largely developed ; and in other places the shales predominate ; but 

 the two elements of the group are usually intermixed, and alternate 

 with one another indefinitely. At some localities, again, as at Ash 

 Gill, near Torver, and at the head of Appletreeworth Beck, the shales 

 are largely developed at the expense of the limestone, and are suffi- 

 ciently thick to have been extensively worked for slates. At Keisley, 

 near Dufton, again, the series is almost calcareous, and the shales 

 appear to be entirely confined to its upper portion. Finally, at 

 Beck and Waterblain, near Millom, the group consists of an upper 

 series of cleaved fossiliferous shales, in the lower part of which a 

 great thickness of limestone is developed, dis continuously, in the 

 form of great lenticular masses of a purely calcareous nature. 



In its intimate characters the limestone of the Coniston Limestone 

 group differs greatly in different localities. Usually it presents 

 itself as a hard, compact, greyish blue, grey, or nearly black lime- 

 stone, which, in thin sections prepared for the microscope, exhibits 

 a subgranular matrix in. which fragments of Crinoids, Corals, or 

 Brachiopods are imbedded at intervals. At Keisley (fig. 2), where 

 we have most carefully examined it, three principal varieties may be 

 distinguished : — (1) a hard, compact, greyish blue limestone with the 

 microscopic characters and general aspect of the ordinary variety of 

 the limestone just alluded to ; (2) a reddish or pink compact marble 

 with numerous patches of white calcite, both portions of the mass 

 appearing, in microscopic sections, to be crowded with minute organ- 

 isms and fragments of larger fossils ; (3) a light- coloured, whitish 

 blue or white, coarsely crystalline limestone, which is seen, in thin 

 sections, to be composed of innumerable fragmentary organic remains 

 and microzoa ; imbedded in transparent calcite, and having large 

 crystals of calc-spar with their characteristic cleavage-lines shooting 

 through the mass in various directions. 



Fig. 2. — Sketch Section of the Coniston Limestone at Keisley, near 

 Dufton. (Length rather more than one third of a mile.) 



Fault. 



Jsi'.N.W. 



Keisley. 



High-Cup- Pennine 

 Gill Beck. Fault. 



S.S.B 



a. Borrowdale series. b. Coniston Limestone. 



c. Barren ground, occupied in whole or in part by the Graptolitic 



mudstones. 



d. Knock beds (pale slates). p. Permian strata. 



