Discussion.
Prof. Hughes regretted that the more important fossils were not upon the table, as he thought an examination of them, or of the matrix, might suggest some explanation of the difficulties. He questioned the discovery of Orthis vespertilio, Trinucleus, &c. in the Graptolitic Mudstones; and with regard to the sections drawn by the authors, he said he had not carried away quite the same impression of the stratigraphical position of the beds in the area described. He thought that the Coniston Limestone could seldom be considered as one distinct mass of limestone, but that concretionary bands of varying thickness and number appeared at various horizons in a mass of shale in which different fossils locally prevailed at different horizons. By this kind of evidence it was almost but not quite certain that the Graptolitic Mudstones and their basement-beds did rest on different parts of the Lower Series, e.g. at Skelgill, on the limestone bands, and near Coniston, on the Ash-Gill Flags. In the Craven district he had found a conglomerate at the base of the Coniston-Ulag Series, but no Graptolitic Mudstones. In the Sedbergh district a similar conglomerate seemed distinctly to underlie the Graptolitic Mudstones. He allowed that the facies of the Graptolites was very like that of the Lower Series, but pointed out that Barrande had got the very same group in his E, e, i at the base of his Upper Series.
He further pointed out that there were in North Wales two sets of pale slates, one near the top of the Lower Series, the other near the base of the Upper, and probably derived at second hand from older volcanic rocks. Only the Upper were well marked in the Lake-district; and these were the Knock beds of the authors.
Mr. De Rance stated that he had spent two years in mapping the rocks of the Volcanic (Borrowdale) series underlying those under consideration. He agreed with Prof. Hughes, that the fossiliferous calcareous band referred to by the authors belonged to the Coniston Limestone, and not to the underlying volcanic rocks, as stated by them. And he remarked that in tracing the outcrop of the Coniston Limestone across country, it was found to rest upon different and successive members of the underlying volcanic series, which plunge under it with varying direction of strike and amount of dip, the unconformity being so marked between the two sets of rocks that occasionally the volcanic series appear to have obtained a dip, been denuded, and faulted before the deposition of the overlying Coniston series.
Mr. Hicks differed from Prof. Hughes as to the value of the paper, which he regarded as at all events opening a question on which other observers might be induced to bring forward their views. He inquired whether Mr. De Rance's statements showing unconformity at the base of the Coniston series did not conflict with the views of Prof. Hughes. He thought that there was no occasion to be surprised at repetitions of beds in such a district. In some sections there is no visible unconformity between the base of
