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REPORT—1875. 3 Llandovery. He criticised the palaeontological and other evidence upon which this division had been made, and protested against the introduction of the name Llandovery Rocks instead of May-Hill Sandstone, under which it was first de scribed by Prof. Sedgwick. In the Lake-district and in North Wales in every open section there was an apparent conformity, though the overlap of the Graptolitio mudstone, from the Ooniston Limestone of Windermere to the Ash-Gill Flags^ of Coniston, seemed to suggest an unconformity. The May-Hill Sandstone, thinning out to the north and creeping over the edges of the Cambrian rocks and along the ancient mountain-range of the Malvern and Longmynd, rests on the oldest parts of the Cambrian and even on the pre-Cambrian. Still this cannot be said to repre sent the previous denudation of the whole thickness of the Cambrian rocks, as they themselves thin out against the old Malvern ridge ; so that this epoch would appear to have been characterized in the typical regions by the upheaval of some mountain- chains and irregular movements in large adjoining areas. 9th Epoch. Silurian.—This series he thought commenced with the base of the May-Hill Sandstone (». e. at the bottom of the Lower Llandovery, with some cor rections of boundary). There was a very considerable change in the forms of life, and this was conspicuous even where the stratigraphical discordance was not well marked. There was little difference of opinion as to the grouping of beds, except at the commencement and clo3e of the period. Conglomerates mark the base at Austwick and Sedbergh, on the western borders of the Lake country, accompanied by a change in the character and colour of the sddiment and of the organic remains. The boundary can be traced through the Lake-district proper, and in North Wales by the same change in the fossils and the sediment, but there is no conglomerate. In South Wales a conglomerate frequently marks the base ; but the group of fossils that comes on first is very different, and seems to suggest an earlier submergence of the southern area. Passing over the Wenlock and Ludlow, the next difficulty is in drawing the upper boundary. This he would take at the top of the red shales and marls of the river Sawdde and the country east of Horeh Chapel in South Wales ; for there is no evidence of a break there or anywhere else between the tilestones and the red shales; and where fossils have been found, as at Ledbury, in the red shales they are common Ludlow forms. The author pointed out, by reference to original and published sections by Prof. Sedgwick, that the views he now advocated as to the classification of the Cam brian rocks and the position of the boundary-line between them and the Silurian were exactly those of Prof. Sedgwick. He further showed, by comparison of the map and sections of Murchison with those of the Survey and later authors, that Murchison had not, in 1839, correctly placed any one of the beds about which he later came into collision with Sedgwick ; that the Caradoc of Murchison's sections, supposed to rest on the Llandeilo Flags south of Llandeilo, was May-Hill Sandstone or Wenlock; that the Cambrian rocks, supposed by Murchison to crop out from below the Llandeilo Flags, were Caradoc and newer beds overlying it; that the supposed base of the Llandeilo Flags was in fact the top. He further stated that when these errors were corrected there was no acknowledgment of the approach made in the new editions to the original classification of Sedgwick; that the latest change had carried the base of the Silurian below the unconformities in the Cambrian rocks given in vol. iii. of the ‘ Memoirs of the Geological Survey,’ and had left it where he thought no one would now venture to suggest there was any palaeontological or stratigraphical break. As this must be changed, and the unconformities above mentioned would, he thought, be certainly abolished before long, he asked whether for justice and consistency we should not, in adopting Prof. Sedgwick’s classifica tion, adopt his nomenclature also. 10th Epoch. The Gap between the Silurian and Carboniferous.—This he con sidered one of the two most strongly marked gaps (except, possibly, some pre- Cambrian intervals) in all the geologic series. In the north of England the Cambrian and Silurian rocks were folded and denuded down to the Skiddaw Slates: strata to the thickness of at least five or six miles were removed. In the north-west of Wales a similar denudation seems to have been going on ; but as we turn to the east wo find, along the Yale of Clwyd for instance, that thera
