284 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC. 13, 



which Ues between the northern flexure of the Po, and the wall of 

 crystalline and eruptive rocks which form the edge of the Alps, a great 

 group of true cretaceous and older eocene formations may have for- 

 merly existed ; but of these no traces now remain. The oldest rocks 

 visible are those which, on the right bank of the Po, range from 

 Gassino by Casal Borgone and the hills south of Verrua ; in other 

 words, they form the northern limit or escarpment of the Monferrato. 

 Amid the sandy marls which there abound, certain peculiar and 

 mottled limestones protrude, either in vertical or highly inclined 

 positions, which, because they seem at one spot to have a certain di- 

 rection and contain nummulites, have been described as cretaceous 

 by M. Collegno* and by M. Sismonda. Since those authors wrote, 

 the Marquis Pareto has in my opinion taken the true view of the 

 subject, and has considered these beds to be tertiary and intimately 

 associated with the miocene of the Superga. 



Accompanied by the two excellent palaeontologists of Turin, Dr. E. 

 Sismonda and M, Bellardi, I made a transverse section of the ridge to 

 the east of the ground which I had examined twenty years ago in com- 

 pany with Sir C. Lyell ; and a simple description of this section will 

 I hope set at rest the question as to the age of the lowest visible 

 rocks in these ridges, and also indicate a gradual transition upwards 

 into younger tertiary strata. In ascending the hill-side from the 

 banks of the Po near Gassino, I found that micaceous marls dip 

 south, and afterwards become vertical and graduate into calcareous 

 sandstone locally called molasse. After passing over a slope obscured 

 by vegetation, other sandy marls are seen to reappear at a higher 

 level in vertical positions, and enclosing an equally vertical band of 

 mottled, small concretionary limestone with nummulites {g of fig. 36), 

 which strikes N.N.E. and S.S.W. A short interval is occupied by 

 strata of green-grained marlstone with some imperfect minute plants, 

 when there follows another and much stronger band of about 1 2 feet 

 thick of similarly mottled, subconcretionary, blue-hearted limestone, 

 which, striking from W.S.W. to E.N.E,, plunges to the S.S.E. at an 

 angle of from 50° to 60°, and is covered by impure limestone or cal- 

 careous sandstone. Ascending over a few undulating mounds of marl 

 and sandstone (the site of old quarries where the limestone has been 

 extracted), the same band of mottled limestone is met with, dipping 

 at a high angle to the north. 



To decide upon the age of this limestone {g of fig. 36), as M. Col- 

 legno has attempted to do, by noting the direction of any one of its 

 broken masses, seems to me futile. Sufiice it to say, that the chief 



* Memoires de la Soc. Geol. de Fr. vol. ii. p. 203. M. Collegno has also coloured 

 in as cretaceous the whole of the eastern end of the Monferrato from Verrua to 

 Casale, for which he has no better authority than the occasional reappearance of 

 the Gassino limestones, sometimes with, sometimes without nummulites. I regret 

 much that I bad not time to explore the eastern part of the Monferrato, in which 

 M. Collegno lays down a much broader mass of what he calls cretaceous ; for 

 judging from all other analogies, and even from what he writes himself, I have 

 little doubt that downward passages thei'e exist into the true eocene or equivalent 

 of the flysch of the Alps ; such rocks being, in fact, a part of the cretaceous group 

 of that author. 



