450 Dr. Du Riche Preller—Ophiolithic Rocks, W. Liguria. 
Cogoleto and Arenzano the sequence is normal, the dolomitic lime- 
stone and quartzite here being, moreover, as Rovereto has shown, 
underlain by Lower Triassic quartzite and conglomerate and Permian 
schist as the substratum. Another curious phenomenon is the 
wedge of cale-schist, quartzite, and mica-schist which projects from 
the belt of these rocks on the coast into the pietre verdi area north of 
Voltri for about 12 kilometres to Mele, the Turchino Pass, and beyond 
to Masone and Campoligure. This wedge, very similar to the 
Santuario island in the Savona region, is up to 4 kilometres wide, 
and divides the Voltri group on the Ligurian side into two unequal 
parts. Except an outcrop of serpentine in the Stura Valley 
immediately north of the road-tunnel on the Turchino Pass, it is 
practically denuded of pietre verdi. 
The Eocene formation east of the contact line and thence to the 
Polcevera Valley, north of Genoa, is composed as usual of fossiliferous 
(Helminthoidea) limestone, argillaceous, often shaly schist, and macigno 
sandstone. It is in the argillaceous schist between Cornigliano and 
Sestri, viz. between the Polcevera and Chiaravagna Valleys, that 
occurs the mass of ophiolithic rocks which extends from the headland 
of S. Andrea north to Borzoli and Madonna della Guardia for about 
8 and 2 kilometres in length and width, while further north several 
smaller masses crop out at S. Martino, near the Bocchetta Pass, and 
between the latter and Voltaggio, forming a fringe round the eastern 
margin of the Voltri group. As in the Savona region, so also in the 
Voltri area deposits of Oligocene conglomerate and breccia are frequent 
and extensive, one of the largest being a bank 500 metres in thickness 
in the Morsone Valley near Voltaggio, which is entirely composed of 
pietre verdi débris. 
The relation of the Voltri group to the adjacent one of Sestri and 
Isoverde has been the aul ect of considerable controversy. De Stefani’ 
and Termier & Boussac® regard the Voltri group as an integral part, 
not of the Alps, but of the Apennines. In Termier and Boussac’s 
view there is between the two sedimentary and ophiolithic formations 
no division or discontinuity, but a gradual passage from Triassic to 
Post-Triassic, the former being simply more metamorphosed than the 
latter, and both constituting a consecutive series after the pattern 
of the French Alpine séries compréhensives. Sacco assigns the 
argillaceous schists and the macigno sandstone, including the ophio- 
lithic rocks of the Sestri and Isoverde group, to the Cretaceous, and 
the uppermost fossiliferous (Helminthoidea) limestone strata to the 
Lower Eocene.? The weight of evidence is, however, largely in 
favour of a distinct difference and division between the two un- 
conformably juxtaposed sedimentary and ophiolithic formations, the 
Voltri group being Triassic and that of Sestri and Isoverde prevaiently 
1 ©. De Stefani, ‘‘ La zona serpentinosa della Liguria occidentale ’’: Rendi- 
conti Atti R. Acc. Lincei, Roma, 1913, pp. 547 and 661 et seq. 
2 Pp. Termier & J. Boussac, ‘‘ Passage latéral N.O. de Génes de la série 
cristallophyllienne (schistes lustrés) 4 la série sédimentaire-ophiolitique de 
l’Appennin ’’?: Comptes Rendus Acc. Sciences, Paris, 1911, p. 1361 et seq. 
°F. Sacco, ‘‘L’Age des formations ophiolitiques récentes’’: Bull. Soc. 
belge de Géol., vol. v, 1891. Carta geologica Appennino centrale 1 : 100,000, 
Torino, 1891. 
