156 Professor Hausmann on the Geognostical Structure 
Finale , in conformable and alternating beds with compact lime- 
stone and clay-slate , from whence we may conclude that this 
mica-slate belongs truly to the transition formation. Our 
author also considers it as probable, that the gneiss observed on 
the same coast by Saussure, is of the same age with the rocks 
just mentioned, which is not without plausibility, on recollecting 
that transition-gneiss has been shewn to occur in many parts in 
the Alps. 
Compact limestone occurs very abundantly in alternating beds 
with the greywacke and clay-slate. Sometimes it appears in 
great masses, but more frequently in alternating beds with these 
and other transition-rocks. In this manner it occurs in many 
places of the Appennines of Genoa, particularly on the rocky 
coast extending from Genoa to the Gulph of Spezia, where it 
displays numerous wavings, and also fine sections of its strata. 
It also occurs on the southern declivity of the Appennines to the 
neighbourhood of Florence, from whence it extends westwards 
into Sienna. When the compact limestone comes in contact with 
the greywacke and clay-slate, it passes more or less completely 
into these rocks; and in this way, a calcareous clay-slate is 
formed, which occurs in considerable masses in the upper Ap- 
pennines, as it does in the Alps. 
The stone known in Florence under the name Pietra forte , and 
used as flagstones for the streets, is a limestone, mixed with quartz 
and mica, which occurs in beds along with the greywacke of that 
quarter. The grey colour, which is so characteristic of transi- 
tion limestone, is that which occurs most frequently in the lime- 
stone of the Appennines. Many other colours also occur ; and of 
these coloured varieties, one of a brownish-red, and mixed with 
clay-slate, found in the neighbourhood of Sienna, is used for orna- 
mental purposes. The compact transition limestone of the Ap- 
pennines contains very few organic remains. Micheli found an 
ammonite in it ; and this rare specimen is now in the cabinet of 
Professor Targioni Tozzetti at Florence. The most remarkable 
of all the limestones of the Appennines is the hrecciated , which oc- 
curs in single beds, and in mountain masses of considerable magni- 
tude, as at Carrara , Mass a, and Seravezza. The beautiful brec- 
ciated marble of Seravezza is of this description. The rock appears 
as if composed of fragments of limestone, varying in size, also in 
