TRUE VOLCANOES. 447 



of Eifel, as I have already observed, both from the activity 

 which once manifested itself in the Maars (or mine-funnels) 

 sunk in the Devonian-schist, and that shown in the raised 

 structures from which lava-streams flow, as on the long ridge 

 of the Mosenberg and Gerolstein. The surface does not here 

 indicate what is hidden in the interior. The absence of tra- 

 chyte in volcanoes which were so active thousands of years 

 ago, is a still more striking phenomenon. The augitiferous 

 scoriae of the Mosenberg, which partly accompany the basaltic 

 lava-stream, contain small burnt pieces of schist, but no 

 fragments of trachyte, and in the neighbourhood the tra- 

 chytes are absent. This species of rock is only to be seen 

 in the Eifel in a state of entire isolation 63 far from the Maars 

 and lava-yielding volcanoes, as in the Seliberg at Quiddel- 

 bach, and in the mountain-chain of Reimerath. The different 

 nature of the formations through which the volcanoes force 

 their way so as to operate with power on the outer crust of 

 the earth is geologically as important as the material which 

 they throw out. 



The conditions of configuration in those rocky structures 

 through which volcanic action manifests itself, or has en- 

 deavoured to do so, have at length been in modern times far 

 more completely investigated and described in their often 

 very complicated variations in the most distant quarters of 

 the globe than in the previous century, when the entire 

 morphology of volcanoes was limited to conical and bell- 

 shaped mountains. There are many volcanoes whose confi- 

 guration, altitude and range (what the talented Carl Frie- 

 drich JSTaumann calls the geotectonics), 64 we now know in 

 the most satisfactory manner, while we continue in the 

 greatest ignorance regarding the composition of their diffe- 

 rent rocks and the association of the mineral species which 

 characterise their trachytes, and which are recognisable 



63 See above, pp. 2326. 



64 The fullest information we possess on any volcanic district, founded 

 on actual measurements of altitudes, angles of inclination, and profile 

 views, is contained in the beautiful work of the Astronomer of Olmiitz, 

 Julius Schmidt, on Vesuvius, the solfatara, Monte Nuovo, the Astroni, 

 Eocca Monfina and the old volcanoes of the Papal territory (in the A> 

 banian Mountains, Lago Bracciano, and Lago di Bolsena). See his hyp- 

 Eometrical work, Die Eruption dcs Vcsuvs im Mai, 1855, with Atlas, 

 plates iii, iv. iz. 



