224 cosmos. 



craters, but more to the northwest. The average elevation 

 of the Maars of the Eifel above the surface of the sea falls 

 between 922 feet (Laacher lake?) and 1588 feet (Mosbrucher 

 Maar). 



As this is peculiarly the place in which to call attention 

 to the uniformity and agreement exhibited by volcanic ac- 

 tivity in its production of material results, in the most dif- 

 ferent forms of the outer frame- work (as Maars, as circum- 

 vallated craters of elevation, or cones opened at the sum- 

 mit), I may mention the remarkable abundance of crystal- 

 lized minerals which have been thrown out by the Maars in 

 their first explosion, and which still in part lie buried in the 

 tufas. In the environs of the Laacher lake this abundance 

 is certainly greatest ; but other Maars also, for example the 

 Immerather, and the Meerfelder Maar, so rich in bombs of 

 olivin, contain fine crystallized masses. We may here men- 

 tion zircon, hauyne, leucite,* apatite, nosean, olivin, augite, 

 ryacolite, common feldspar (orthoclase), glassy feldspar (san- 

 idine), mica, sodalite, garnet, and titanic iron. If the num- 

 ber of beautifully crystallized minerals on Vesuvius be so 

 much greater (Scacchi counts 43 species), we must not for- 

 get that very few of them are ejected from the volcano, and 

 that the greater number belongs to the portion of the so- 

 called eruptive matters of Vesuvius, which, according to the 



* Leucite (of the same kind from Vesuvius, from Rocca di Papa in 

 the Albanian mountains, from Viterbo, from the Rocca Monfina, ac- 

 cording to Pilla, sometimes of more than three inches in diameter, 

 and from the dolerite of the Kaiserstuhl, in the Breisgau) occurs also 

 "in position as leucite-rock in the Eifel, on the Burgberg, near Rie- 

 den. The tufa in the Eifel incloses large blocks of leucitophyre near 

 Boll and Weibern." I can not resist the temptation to borrow the 

 following important observation from a chemico-geognostic memoir 

 read by Mitscherlich a few weeks since before the Academy of Ber- 

 lin : "Aqueous vapors alone may have effected the eruptions of the 

 Eifel, but they would have divided olivin and augite into the finest 

 drops and powder if they had met with them in a fluid state. With 

 the fundamental mass of the erupted matters fragments of the old, 

 broken-up rock are most intimately mixed, for example, on the Drei- 

 ser Weiher, and these are frequently caked together. The larger ol- 

 ivin masses and the masses of augite even usually occur surrounded 

 by a thick crust of this mixture ; a fragment of the old rock never oc- 

 curs in the olivin or augite ; both were consequently formed before 

 they reached the spot where the breaking up took place. Olivin and 

 augite had, therefore, separated from the fluid basaltic mass before 

 this met with an accumulation of water or a spring which caused its 

 expulsion." See also upon the bombs an older memoir by Leonard 

 Horner, in the Transactions of the Geological Society, 2d series, vol. 

 iv., pt. 2, 1836, p. 467. 



