│Upper or Silurian │Ludlowian (Murchison Silurian Period. │ (Murchison, restricted, │ 1839). │ 1835). │ „ │ „ │Wenlockian (Murchison │ │ 1839). „ │ „ │Landoverian (Murchison). ─────────────────┼──────────────────────────┼────────────────────────── „ │Middle or Ordovician │Caradocian (Murchison │ (Lapworth 1879). │ 1839). „ │ „ │Landeilian (Murchison │ │ 1839). „ │ „ │Arenigian (Sedgwick 1847). ─────────────────┼──────────────────────────┼────────────────────────── │Lower or Cambrian │ „ │ (Sedgwick, restricted, │Potsdamian (Emmons 1838). │ 1835). │ „ │ „ │Menevian (Salter and Hicks │ │ 1865). „ │ „ │Georgian (Hitchcock 1861). Regarding this period, which, by the way, is not very unlike that of Barrande, Renevier remarks that it is “as important as the Cretaceous or the Jurassic. Lapworth even gives it a value of the first order equal to the Protozoic era.” In the above there is an obvious objection in the double usage of the term Silurian, and this difficulty was met later on in Lapparent’s Traité by the proposal to substitute Gothlandian for Silurian. Of this change Geikie remarks: “Such an arrangement ... might be adopted if it did not involve so serious an alteration of the nomenclature in general use.” On the other hand, if diastrophism and breaks in the stratigraphic and faunal sequence are to be the basis for geologic time divisions, we cannot accept the above scheme, for it recognizes but one period where there are at least four in nature. _Conclusions._—We have arrived at a time when our knowledge of the stratigraphic and faunal sequence, plus the orogenic record as recognized in the principle of diastrophism, should be reflected in the terminology of the geologic time-table. It would be easy to offer a satisfactory nomenclature if we were not bound by the law of priority in publication, and if no one had the geologic chronology of his own time ingrained in his memory. In addition, the endless literature, with its accepted nomenclature, bars our way. Therefore with a view of creating the least change in geologic nomenclature, and of doing the greatest justice to our predecessors that the present conditions of our knowledge will allow, the following scheme is offered: Silurian period. Llandovery to top of Ludlow in Europe. Alexandrian-Cataract-Medina to top of Manlius in America.