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, 6, 

 from the denuded clay c. 



Hills of Mont Ferrat and the Superga. The late Signer 

 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 J. 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. 

 J See section, wood-cut No. 4 ; p. 21. 



P 2 



