60 REPORT — 1853. 



concludes, that in no part of Wales, or the adjacent counties, is there any one con- 

 tinuous unbroken section through which we can ascend from the Cambrian to the 

 Silurian groups. There is a physical break between them ; and in very near coordi- 

 nation with that break (often marked by a discordancy of position) there is a great 

 change in fossil species. The author showed the bearing of these views on the sec- 

 tions from the Ciea Hills to the Longmynd, and on similar sections from the vicinity 

 ofLlandeilo ; and from both districts drew confirmations of his conclusion, //i«< all the 

 oldei- groups of North and South Wales, and of a part of the Silurian district, up to the 

 base of the May Hill sandstone, must retain the name ' Cambrian,' which has the 

 claim of priority, is geographically true, and palieontologically right. 



The author, after referring to the history of the investigations into the Silurian 

 and Cambrian systems, remarks that he never had the expectation of establishing, by 

 the evidence of fossils, a separation between Cambrian and ' Lower Silurian' rocks, 

 which has been attributed to him. He had from the first a contrary opinion, founded 

 both on sections and fossils. 



That the fossils of the whole Bala group and the fossils of Snowdonia were iden- 

 tical with the fossils of the so-called Lower Silurian groups, was certain long before 

 there was any matter of dispute about the Paleozoic nomenclature ; but that was 

 considered by the author as no reason for extending the Lower Silurian nomenclature 

 over all the older groups of Wales. It was, however, a very (jood reason for keeping 

 the Lower Silurian nomenclature in abeyance ; and pretending to no strictly defined 

 nomenclature of Lower Silurian or Upper Cambrian rocks, till it could be permanently 

 fixed both by true sections and corresponding groups of fossils. That period it has at 

 length reached through the determination of the May Hill group ; which group was 

 introduced, or immediately preceded, by great physical movements indicated here and 

 there by great masses of conglomerate, by great groups of rock with a new physical 

 type, and generally in a position discordant to the Cambrian series ; and at the same 

 time by a great change in the organic types ; i. e. by the sudden disappearance of 

 the undoubted Cambrian types, and by the sudden appearance of undoubted Silurian 

 types. Such phsenomena may well be considered as the prelude to a new system or 

 a new series of physical groups demanding a separate name. The scheme of no- 

 menclature and classification, given in this communication, does not deprive the 

 ' Silurian System ' of a single stratum or a single group of fossils which belong to it 

 on a right and natural interpretation of the sections. At the same time, the original 

 Silurian map is on this scheme not greatly changed. The groups of Caer Caradoc 

 and Llandeilo become indeed absorbed in the upper Cambrian groups, among which 

 they find their true geographical and true sectional place ; but the greater part of the 

 rocks hitherto called Caradoc sandstone still have their place in the map of Siluria 

 under another name (May Hill sandstone). The remarkable groups of Tortworth 

 and the Usk ; all the groups of May Hill and Woolhope ; all the Silurian groups on 

 the west side of the Malvern Hills (with an almost evanescent exception at Holly 

 Bush) ; the groups of Abberley, Presteign, Aymestry, and Ludlow ; all these groups 

 will remain almost untouched, or with one new Silurian colour for the May Hill beds. 

 A distinct colour for the May Hill sandstone must appear at the base of Wenlock 

 Edge. Further north the changes in the Silurian map will be more considerable ; 

 but it will be compensated, for the loss of certain Cambrian groups, by a large ex- 

 tension of the May Hill sandstone through the chain of the Berwyns, and thence, as 

 in the Government map (iu which it is laid down under the erroneous name of " Middle 

 Silurian"), to the sea near Conway. 



The author then compares with the results of his investigation the nomenclature 

 and classification adopted in the publications of the Geological Survey of Great 

 Britain, in which only those lower groups which are without fossils are ranked as 

 ' Cambrian'. He objects to the extension of the meaning of ' Llandeilo rocks,' so as 

 to make them comprehend the Upper and Lower groups of Bala ; and to the use of 

 such a term as ' Middle Silurian,' embracing the May Hill and Caradoc sandstones. 

 The distinction of these two sandstones was first made out in the Cambridge Mu- 

 seum by Professor M'Coy, after a detailed examination of the Cambrian and Silu- 

 rian fossils collected by the author ; it has since been confirmed by an examination of 

 sections in the field ; and the author believes there is no alternation of Cambrian and 

 Silurian rocks, no confusion of these separate groups, and no well-defined great 

 ' middle ' group, blending the characters of the two extremes. He claims the right 



