268 COSMOS. 



rence of a vast number of beautiful and most various crystals^ 

 as garnets, vesuvian, augite, and ceylanite, on the surfaces of 

 contact between the erupted and sedimentary rock, as for 

 instance, on the junction of the syenite of Monzon with 

 dolomite and compact limestone.* In the Island of Elba 

 masses of serpentine, which perhaps nowhere more clearly 

 indicate the character of erupted rocks, have occasioned the sub- 

 limation of iron glance and red oxide of iron in fissures of cal- 

 careous sandstone. t We still daily find the same iron glance 

 formed by sublimation from the vapours and the walls of the 

 fissures of open veins on the margin of the crater, and in the 

 fresh lava currents of the volcanoes of Stromboli, Vesuvius, 

 and Etna. | The veins, that are thus formed beneath our 

 eyes by volcanic forces, where the contiguous rock has already 

 attained a certain degree of solidification, show us how in a 

 similar manner mineral and metallic veins may have been 

 everywhere formed in the more ancient periods of the world, 

 where the solid but thinner crust of our planet, shaken by 

 earthquakes, and rent and fissured by the change of volume 

 to which it was subjected in cooling, may have presented 

 many communications with the interior, and many passages 

 for the escape of vapours impregnated with earthy and 

 metallic substances. The arrangement of the particles in. 

 layers parallel with the margins of the veins, the regular 

 recurrence of analogous layers on the opposite sides of the 

 veins, (on their different walls), and. finally, the elongated 

 cellular cavities in the middle, frequently afford direct evi- 

 dence of the plutonic process of subli ' nation in metalliferous 

 veins. As the traversing rocks mast be of more recent 

 origin than the traversed, we learn from the relations of 



* Leop. von Buch, Briefe, s. 109-129. See also Elie de Beaumont, 

 On the contact, of Grcnite with the Beds of the Jura, in the Mem. geol., 

 t ii. p. 408. 



f Hoffman, Eeise, s. 30 und 37. 



t On the chemical process in the formation of specular iron, see Gay- 

 Tjussac, in the Annales de Chimie, t. xxii. p. 415, and Mitscherlich, in 

 Poggend. Annalen, bd. xv. s. 630. Moreover, crystals of olivine have 

 been formed (probably by sublimation) in the cavities of the obsidian 

 of Cerro del Jacal, which I brought from Mexico (Gustav Rose, in Pog- 

 gend. Annalen, bd. x. s. 323). Hence olivine occurs in basalt, lava, 

 obsidian, artificial scoria;, in meteoric stones, in the syenite of Elfdaie, 

 tnd (as hyalosiderite) in the Wacke of the Kaiserstuhl 



