Ch. XV.] MONT FERRAT AND THE SUPERGA. 211 
Were upheaved to their present height, a pause which allowed 
time for the sea to advance and strip off the upper beds a, b, 
from the denuded clay c. 
Hills of Mont Ferrat and the Superga. — The late Signor 
Bonelli of Turin was the first who remarked that the tertiary 
shells found in the green sand and marl of the Superga near 
Turin differed, as a group, from those generally characteristic 
of the Subapennine beds. The same naturalist had also ob- 
served, that many of the species peculiar to the Superga were 
identical with those occurring near Bordeaux and Dax. The 
strata of which the hill of the Superga is composed, are inclined 
at an angle of more than 70 degrees. They consist partly of fine 
sand and marl, and partly of a conglomerate composed of pri- 
mary boulders, which forms a lower part of the series, and not, as 
represented by M. Brongniart by mistake % an unconformable 
and overlying mass f. This same series of beds is more largely 
developed in the chain of Mont Ferrat, especially in the basin 
of the Bormida. The high road which leads from Savona to 
Alessandria intersects them in its northern descent, and the 
formation may be well studied along this line at Carcare, Cairo, 
and Spinto, at all which localities fossil shells occur in a bright 
green sand. At Piana, a conglomerate, interstratified with this 
green sand, contains rounded blocks of serpentine and chlorite 
schist, larger than those near the summit of the Superga, some 
of the blocks being not less than nine feet in diameter. 
When we descend to Aqui, we find the green sand giving 
place to bluish marls, which also skirt the plains of the Tanaro 
at lower levels. These newer marls are associated with sand, 
and are nearly horizontal, and appear to belong to the older 
Pliocene Subapennine strata]:. The shells which characterize 
the latter, abound in various parts of the country near Turin ; 
but that region has not yet been examined with sufficient care 
to enable us to give exact sections to illustrate the superpo- 
* Terrains du Vicentin, p. 26. 
f I examined the Superga in company with Mr. Murchison in 1828. 
% See section, wood-cut No. 4, p. 21. 
P 2 
