238 COSMOS. 



whole of this microcosm is of fresh- water formation, and 

 marine Polythalamia 95 only show themselves exceptionally in 

 the uppermost deposit of the friable, yellowish loess at the 

 foot and on the declivities of the Siebengebirge (indicating 

 its former brackish coast-nature). 



Is the phenomenon of Maars limited to Western Ger- 

 many ? Count Montlosier, who was acquainted with the 

 Eifel by personal observations in 1819, and who pronounces 

 the Mosenberg to be one of the finest volcanoes that he ever 

 saw, (like Rozet) regards the Gouffre de Tazenat, the Lac 

 J?avin and Lac de la G-odivel, in Auvergne, as Maars or 

 craters of explosion. They are cut into very different kinds 

 of rock, in granite, basalt, and domite (trachytic rock), and 

 surrounded at the margins with scoriae and rapilli. 96 



The frameworks which are built up by a more powerful 

 eruptive activity of volcanoes, by upheaval of the soil and 

 emission of lava, appear in at least six different forms, and 

 reappear with this variety in their forms in the most distant 

 zones of the earth. Those who are born in volcanic districts 

 amongst basaltic and trachytic mountains, are often genially 

 impressed in spots where the same forms greet them. 

 Mountain forms are amongst the most important deter- 

 mining elements of the physiognomy of nature, they give 

 the district either a cheerful, or a stern and magnificent cha- 

 racter, according as they are adorned with vegetation or sur- 

 rounded by a dreary barrenness. I have quite recently endea- 



95 Upon the antiquity of formation of the valley of the Rhine, see 

 H. von Dechen, Geognost. Besdireibung des Siebengebirges, in the Ver- 

 handl. des Naturhist. Vereins der Preuss. Rheinlande und Westphalens, 

 1852, s. 556 559. The infusoria of the Eifel are treated of by 

 Ehrenberg in the Monatsber. der Akad. der Wiss. zu Berlin, 1844, 

 e. 337, 1845, s. 133 and 148, and 1846, s. 161171. The Trass of 

 Brohl, which is filled with crumbs of pumice-stone containing infusoria, 

 forms hills of as much as 850 feet in height: 



96 See Rozet, in the Memoires de la Societe Geologique, 2me serie, t. i, 

 p. 119. On the island of Java also, that wonderful seat of multifarious 

 volcanic activity, there occur " craters without cones, as it were flat 

 volcanoes" (Junghuhn, Java, seine Gestalt und Pflanzendecke, Lief, vii, 

 p. 640) between Gunung Salak and Perwakti, analogous to the Maars 

 as " craters of explosion." Destitute of any elevated margins, they are 

 situated partly in perfectly flat districts of the mountains, have angular 

 fragments of the burst rocky strata scattered around them, and now 

 only emit vapours and gases. 



