160 Professor Hau smarm on the Geognostical Structure 
we shall be convinced, that, in the places where the secondary 
rocks usually interposed between the transition and newer flcetz 
limestones are wanting, there sometimes occurs a connection, a 
gradual transition from the old limestone to the newest limestone 
of the mountain group ; as also, that masses in the midst of the 
younger formation resemble those of the older, and vice versa. if, 
then, it is difficult, in many places in the Appennines, in the vici- 
nity of the transition rocks, to determine to which formation this 
or that mass of white limestone is to be referred, we may refer 
the great portion of it to the white Jura limestone , which appears 
to be one of the most widely distributed of the floetz rocks. If 
this view is correct, then a part of the plain of the Po with the 
Adriatic Sea, is to be considered as a longitudinal valley extend- 
ing from NW. to SE. in this limestone formation. The principal 
boundaries of the Italian rocks run in the same direction. The 
NW. continuation of the line of the white limestone of the Ap- 
pennines above Bologna, meets with the same limestone of Arona 
oil the Lago Maggiore ; the line of the transition formation in 
Calabria skirts Cape Circeo, and advances with increasing breadth 
through the southern part of Tuscany to the upper Appennines, 
and from this onward to the Alps. The line of the primitive 
rocks begins in Southern Calabria, and in the opposite coast of 
Sicily ; touches either the granite of Giglio and Elba, or, if it 
belongs to the transition formation, probably the primitive rocks 
of Capo Corso in Corsica. 
Italy is rich in tertiary rocks, for most of the promontories 
and low hills of the Appennine chain, and also considerable tracts 
of flat country, are composed of them. In general, these rocks 
are sharply separated from the older formations, with which 
they come in contact. B.iit sometimes there also occurs a transi- 
tion from the Appennine limestone into the tertiary masses, as 
was first observed by Brocchi in the territory of Otranto, where 
a white limestone prevails, which contains, besides the Ammo- 
nites of the white secondary limestone, also numerous petrifac- 
tions, which belong only to the tertiary formations. Of these 
tertiary deposites we can distinguish more general , and more 
local formations. To these belong different kinds of marl 9 clay , 
sandstone , coarse conglomerate , and a sand , which is either si- 
liceous or calcareous, and often coloured with hydrate of iron. 
The first mentioned rocks alternate irregularly with each other, 
