18 On the Geology of the Paduan, 
mica than the trachytes of the Mont D’or and Cantal. From an 
excess of these characters, it puts on in some situations the 
aspect rather of a primitive than a volcanic rock, and has thus 
been confounded by M. Da Rio, and, I believe, some other 
writers, with primitive porphyry; a classification from which 
one might imagine its often traversing as dykes, and occasion- 
ally surmounting strata of a secondary lime-stone, full of 
marine shells, would have ensured its exemption. But what 
absurdities are too gross to be resorted to as the last shifts of 
an expiring system? The masegna, like the French trachytes, 
is often accompanied by a trachytic breccia. It is frequently 
eolumnar. ‘The nodular concretions it contains are remarkable, 
some being of pure quartz, others possessing the complete 
characters of hornblende rock, others of a granite, consisting 
of felspar, quartz, mica, and hornblende, in various proportions. 
The felspar is invariably of the glassy sort. 
This variety of trachyte is the prevailing rock throughout the 
Euganean hills. In the Monti Berici, and the low ramifications 
of the Alps which descend towards these, an analogous posi- 
tion is occupied by varieties of basalt, containing imbedded 
crystals of hornblende and olivin, and occasionally some scaly 
grains of felspar. Augite is, as far as my observations go, 
entirely wanting. The basalt is frequently columnar, and 
engravings of the principal ranges in which this structure is 
conspicuous, may be seen in the works of Strange, Fortis, and 
Brieslak. It is generally accompanied by immense accumula- 
tions of a loose or indurated volcanic conglomerate, usually 
under the form of a peperino, and impregnated with calcareous 
or argillaceous particles. 
What is chiefly remarkable in the trap of this district, is its 
being found indifferently both above and beneath strata of the 
old horizontal mountain limestone, which clothes the southern 
face of the Rhetian Alps, and is continued in the mountains of 
Istria and Dalmatia, and which also constitutes the mass of the 
Apennines. In the Valle Nera, near S. Pietro Massolino, I 
convinced myself of the accuracy of the observation made 
there by Strange, viz., the alternation of ¢en distinct beds of 
