Note 1 — Chapter VII · THE VOLCANIC DISTRICT OF THE RHINE VALLEY.
Reading edition
Daubeny, loc. cit., p. 71. The geology of this region has had many investigators, of whom the chief are Steininger, Erloschenen Vulkane in der Eifel (1820); Hibbert, Extinct Volcanoes of the Basin of Neuwied, 1832; Nöggerath, Das Gebirge im Rheinland, etc., 4 vols.; Horner, "On the Geology of Bonn," Transactions of the Geological Society, London, vol. iv.