XXXVlll PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



tion at Hull, explanatory of his views concerning the nomenclature 

 of the Primary formations. The division of the Palaeozoic strata 

 into an Upper, Middle, and Lower series is a natural classification, 

 although some may prefer a twofold instead of a threefold partition. 

 The question concerning the appellations to be given to the subdivi- 

 sions of these three sections, is one which will in the end be deter- 

 mined by custom and the authority of general use. Convenience 

 is eventually the settler of all differences about nomenclature, and 

 even in Zoology and Botany, sciences in which many definite rules 

 are observed with laudable strictness, convenience every now and 

 then overrides all our arbitrary regulations. Professor Sedgwick 

 had previously, during the course of our last session, communicated, 

 in association with Professor M'Coy, certain views of consequence 

 concerning a proposed subdivision of the Caradoc sandstones, which 

 demand a special notice on account of their importance, and because 

 there have been more than one paper on this subject lately read be- 

 fore the Society. The result of these inquiries on the part of several 

 observers is to place the relations of the Caradoc sandstone in a 

 clearer light, both as to strata above and those below it. 



The Caradoc was originally considered by Sir Roderick Murchison 

 as the sandy and upper portion of the Lower Silurian strata. The 

 rocks east of Caer Caradoc presented the best types, and those shown 

 in ascending sections through what are generally called " the Penta- 

 merus beds," to the Upper Silurian, and the arenaceous masses which 

 occupied this position in the Malvern and May Hill districts, were 

 considered by the founder of the Silurian system to be equivalents of 

 at least a part of this series, while they graduated into the Wenlock 

 shale. 



But while our Caradoc sandstone, so constituted, contained in 

 some parts numerous fossils that were Llandeilo species, in its upper 

 portion it was supposed to contain these species mingled with the 

 characteristic Pentameri. Li America the latter fossils were found 

 associated only with species characteristic of the Upper Silurians, and 

 the group of strata containing this assemblage appeared to be cut off 

 distinctly from the underlying Llandeilo rocks. 



The unravelling of this anomaly is in part due to Professor Sedg- 

 wick, and in part to the ofiicers of the Geological Survey. In a com- 

 munication contained in the fourth volume of our Journal, ^Ir. Ram- 

 say and Mr. Aveline have shown that the Pentamerus beds around 

 the Longmynd repose nnconformablvupon the Llandeilo flags, whilst 

 they graduated upwards, as Sir Roderick Murchison had stated, into 

 the Wenlock shale. But here only the upper part of the Caradoc 

 was developed, and this portion contained but few of the Lower Silu- 

 rian species. Li a subsequent paper in our eighth volume, the phy- 

 sical connection of the Upper Caradoc with the base of the "Wenlock 

 shale was definitely and fully stated. In the meantime, and quite 

 independently, Professors Sedgwick and M'Coy examined the Cara- 

 doc beds of May Hill and the Malverns, and became convinced that 

 these beds, containing as they did only Upper Silurian species, must 

 be regarded as the base of the Upper Silurians, and that the Caradoc 



