396 DE. W. HIND AND MR. J. A. HOWE ON THE [Aug. I9OI, 



from the * knoll ' and become embedded in the surrounding shales 

 (see p. 362). No. 346 is from the foot of Keal Hill, and maj' 

 be compared with No. 343 from a similar position near the foot 

 of Stebden Hill, both hills being members of the series of Cracoe 

 ' knolls.' 



VI. Petrology and Micropal^ontology. 



The rocks of the Pendleside Limestone Group from the type-area 

 on Pendle Hill, can hardly be said asawholeto exhibit characters 

 of sufficient peculiarity to be of diagnostic value. This arises from 

 the diversity of structure, composition, and origin among the 

 members of the ^ Limestone.' Indeed, to speak of the ' Pendleside 

 Limestone,' as it is found on Pendle Hill, conveys an erroneous 

 impression of an uniform and well-defined bed or series of beds, 

 instead of which — as was pointed out by the officers of the Geological 

 Survey ^ — we find banded mudstones, black limestones, magnesian 

 limestones, grey limestones, more or less siliceous, and bands of 

 chert. Of these only the black, rather impure beds are found in 

 other districts, and such must be regarded as typical of the 

 Pendleside Limestone Group ; the others may be looked upon as 

 a special local phase in this area of greatest development. 



General Description of the Hocks in the Pendleside 

 Limestone on Pendle Hill. 



Hard Grey Limestones. 



These limestones are best seen in the Clough above Hook Cliff, 

 especially in the upper third of the limestone series. They are 

 all organic in origin : crinoids, foraminifera, sponges, bryozoa 

 and some hydrozoa, with occasional fragments of brachiopod-shells 

 being associated together, sometimes one form, sometimes another 

 preponderating. The organisms frequently appear to have been 

 arranged in beds by the sorting action of gentle currents, for 

 in some beds all the fragments are fairly large, in others they are 

 all quite small : this applies to all the organisms alike. A laminated 

 structure is evident in some of the beds, and is well brought out by 

 weathering in the * anvil-stones.' 



A matrix of clear crystalline calcite is invariably present, and in 

 many places in a thin section is seen to encroach upon and frequently 

 obliterate the organisms. 



Many interesting stages in the alteration of a simply organic into 

 a crystalline calcareous or siliceous rock may be seen in slides cut from 

 these limestones. The arenaceous structure of the walls of some 

 of the foraminifera is generally well shown, their interior being 

 filled with clear calcite. But frequently only the outline remains, 

 enclosing a space of indistinct grey calcareous matter ; Archceodiscus, 

 as usual, retains its walls in a condition of amber-coloured clear 



• Geology of the Burnley Coalfield ' Mem. Geol. Surv. (1875) p. 17. 



