400 Professor Sedgwick and Mr. Murchison on the 



of basaltic lava, containing nests of olivine. The upper part of it is regularly 

 bedded, in which respect, as well as in its whole composition, it bears a close 

 relation to the volcanic conglomerates of Puy en Velay. The summit of the 

 Riegisburg is about four hundred feet above the level of the llaab ; and the 

 capping of volcanic conglomerates seems to be from two to three hundred 

 feet thick. 



The account we have now given of volcanic rocks associated with the 

 youngest tertiary zone, are quite sufficient to explain the nature of their varied 

 geological relations; we, therefore, merely notice their occurrence at Fehring 

 and Kapferstein, where they are in the form of basaltic conglomerates ; at 

 Klausen, where they are basaltic and columnar; and at Seindlberg near Klbch, 

 where they are associated with scoria. 



The juxtaposition of the various volcanic rocks, and their passage into each 

 other in some parts of the region last described, make it difficult, and perhaps 

 impossible, to establish any decisive tests of their relative age, founded upon 

 their mineralogical characters. The newest tertiary group is in one place 

 overlaid by prismatic and basaltic lava ; in anotiier by coarse granular lava, 

 almost passing into trachyte ; in a third by scoria ; and in a fourth, alternates 

 with basaltic tufa and conglomerate. All that we can affirm on this subject 

 is, that the whole of these volcanic rocks were probably produced during the 

 formation of the youngest tertiary deposits of the neighbouring region. 



In igneous rocks of this age we cannot expect to find continuous streams of 

 lava, traceable to the crater from whence they flowed. The form of the country 

 however seems to indicate, as before stated, that the trachytic domes of Glei- 

 chenberg are situated near the principal focus of ancient eruption. Although 

 some of the masses of volcanic rock are so intimately associated with marine 

 deposits, as to leave no doubt of their having assumed their present form under 

 the sea ; yet the great abundance of scoriaceous matter, exactly resembhng 

 the commonest sub-aerial igneous products, led us to infer, that the principal 

 points of eruption rose above the sea which then occupied the basin of Styria *. 



* We did not examine the volcanic region in detail ; and we skirted its western extremity almost 

 exclusively for the purpose of ascertaining the relations of the igneous rocks to the upper tertiary 

 groups. The central trachytic region we merely touched upon. In the hill of Ferish, the alter- 

 nating beds of tertiary sand and volcanic tufa are nearly horizontal ; and certainly did not induce 

 us when on the spot to suppose, that the central trachytes of the Gleichenberg were posterior to 

 all the other igneous products. This hypothesis is, however, supported by Dr. Daubeny; who 

 founds his opinion chiefly upon certain inclined strata, on the Hanks of the Gleichenberg, which did 

 not fall under our observation. See his " Description of Extinct and Active Volcanos," p. 1 10, 



