NOTES. Ixxv 



42 (embracing the Eifel and the Neuwied Basin). On the Maars, see Steininger, 

 Geognostische Beschreibung der Eifel, 1853, S. 113. His earliest, and merito- 

 rious, work, " Die erloschenen Vulkane in der Eifel und am Nieder-Rhein," be- 

 longs to 1820. 



( 317 ) p. 232. Leucite (of the same sort as at Vesuvius, Rocca di Papa in 

 the Alban Hills, Viterbo, Rocca Monfina, according to Pilla sometimes more 

 than three inches in diameter, and in the Dolerite of Kaiserstuhl in the Breis- 

 gau) is also found " in situ as leucite-rock in the Eifel on the Burgberg near 

 Rieden. The tufa in the Eifel encloses great blocks of leucitophyr near Boll and 

 Weibern." I cannot resist the temptation of quoting from manuscript the fol- 

 lowing important remark of Mitscherlich's, contained in a chemico-geological 

 lecture given, a few weeks ago, in the Berlin Academy: " It is only aqueous 

 vapours which can have caused the eruptions of the Eifel ; but these would have 

 divided the olivine and augite into the minutest drops, if they had found them 

 still fluid. In the main mass of the ejected substances, as for example at the 

 Dreiser Weiher, there are intermingled, in the most intimate manner, fragments 

 of the more ancient shattered rock, and which are frequently cemented together. 

 The great masses of olivine and the masses of augite are even, for the most part, 

 surrounded by a thick crust of this mixture ; one never finds in the olivine or in 

 the augite any fragment of the older rock ; both were, therefore, ready formed 

 before they came to the place where the shattering took place. The olivine and 

 augite had, therefore, already separated themselves from the fluid basaltic mass 

 before the latter came into contact with a collection of water or a spring, which 

 brought about an explosive ejection." Compare, respecting the bombs, an earlier 

 memoir by Leonard Homer, in the Transactions of the Geological Soc., 2nd 

 series, vol. iv. Pt. II. 1836, p. 467. 



( 318 ) p. 233. Leop. von Buch, in Poggend. Annalen, Bd. xxxvii. S. 179. 

 According to Scacchi, these ejected substances belong to the first eruption of 

 Vesuvius of the year 79; Leonard's Neues Jahrbuch fiir Mineral., Jahrg. 1853, 

 S. 259. 



( 319 ) p. 236. On the age of formation of the valley of the Rhine, see H. 

 von Dechen, Geogn. Beschr. des Siebengebirges, in the Verhandl. des naturhist- 

 Vereins der Preus. Rheinlande und Westphalens, 1852, S. 556559. Ehren- 

 berg treats of the infusoria of the Eifel in the Monatsberichten der Akad. der 

 Wiss. zn Berlin, 1844, S. 337; 1845, S. 133 and 148; 1846,8.161171. 

 The Trass of Brohl, filled with morsels of pumice containing infusoria, forms 

 hills, in some cases, more than 800 feet high. 



( 32 ) p. 236. Compare Roset, in the Me'moires de la Socie'te' Ge'ologique, 

 2 e se'rie, t. i. p. 119. Also in the island of Java, that wonderful theatre of 



