Vol. 57.] PENDLESIDE GKOFP AT PENBLE HILL, ETC. 379 



The massive limestones of the southern are^ are much richer 

 in their uppermost beds. It is possible that metasomatic chauges 

 in the lower beds may have obliterated man}- fossils, or that the 

 conditions attending their formation were unsuited to molluscan 

 life. So far as our observations have gone, we are unable to say 

 that any part of the great mass is characterized by the presence of 

 sub-zonal forms, or that the lower beds ever contained a rich 

 assemblage of individuals. 



In comparing the life of the Carboniferous Limestone with that of 

 the strata immediately above it, the great importance of corals 

 as rock-builders in the former cannot be overlooked. Indeed, 

 much [oi the limestone, now almost destitute of direct evidence of 

 organisms, may have originated in this way : examination of recent 

 coral-island material certainly goes far towards confirming this view. 

 It is seldom that individual masses of coral measuring more than 

 108(6x6x 3) cubic feet can be found in situ, but in places they 

 are present in such abundance and over such large areas that 

 they must have formed considerable reefs. Even a simple coral, 

 Zaphrentis cylinchnca, for example, occurs at Knocklane Point 

 (Serpent Eock), 2^ miles north-west of Grange in County Sligo, 

 in such enormous numbers as to constitute an extensive deposit. 

 In the Derbyshire limestone corals are plentiful at many horizons, 

 but particularly in the upper 50 feet ; thus, from the top of ilasson 

 Hill towards Winster a well-marked coral-deposit is traced for a 

 distance of over 3 miles. They are common also in the Yoredale 

 Limestones of Wensleydale ; but in the Pendleside Group they are 

 chiefly noticeable by their absence, only a few Zaphrentoid forms 

 being known, of which Z. EnnisJcilleni is the most abundant. 



The most important fact in the faunal distribution of the Pendle- 

 side Limestone Group is the association in these rocks of Posidono- 

 mya Becheri, P. membranacea, Glyjjhioceras sjyirah, Gl. reticulatum,. 

 Posidoniella Icevis, and Avicidojoecten papyraceus. Hitherto Gl. 

 spirale was known only from the Culm Measures of Venn, near 

 Barnstaple, and the Culm of Herborn in Nassau. 



Posidoyiomya Becheri appears to have come in at a slightly earlier 

 period than its associates, for it is found not only in the black beds, 

 as at Budle (Northumberland), and the shales in connection with the 

 Gayle and Hardraw Scar Limestone of Wensleydale, but specimens 

 have been taken from white shelly limestone at Castleton (Derbj'- 

 shire). This constant appearance of P. Becheri, Glyphioceras reticu- 

 latum, and often Gl. spirale, either singly or together, is not merely 

 a local phenomenon, but is found to be the rule in Yorkshire, Lan- 

 cashire, Derbyshire, Cheshire, and Ireland. P. Becheri seems to be 

 restricted vertically to the lower portion of the Pendleside Group, but 

 its associates, Posidoniella Icevis yAvicidopectenpapyraceus,Gastriocera^ 

 Listeri, G. carhonarium, GlypJiioceras bilingue, Gl. reiicidatum, 

 Nomismoceras ornaium, and Dimorphoceras Gilbertsoni, occur again 

 and again. They seem, however, to become extinct with the Middle 

 Coal-Measures, in which they only appear in one or two widely- 

 separated bands. Thus there seems to be evidence for a distinct 



Q. J. G. S. No. 227. 2 i> 



