Why is it that nearly all leading American stratigraphers as well as the authors of the principal American geological text-books—Dana,* Le Conte, † Williams,‡ and Scott§—refer the Lower Helderberg to the Siluric system? This question gains peculiar force when another fact is pointed out, namely, that nearly all European stratigraphers who have investigated the systemic position of the Lower Helderberg, and Geikie,‖ Kayser,¶ and Frech,** in their respective text-books, unhesitatingly place the same formation in the Devonic, as lowest Lower Devonic. This is not merely a question of drawing the line between two geological eras, a little higher or a little lower in the time scale, but it involves taxonomic principles and stages in faunal or evolutional progression.
One of the chief reasons for these varying views lies in the fact that the lower limit of the Devonic of England has never been defined, and . . .