64 Sir R. I. ]\Iurchison on the Vents of Hot Vapour in Tuscany. 



most calamitous shocks iu Sicily and Calabria have occurred when 

 Etna has been most dormant. Putting aside this speculation, the 

 hot vapours may unquestionably be viewed as the remains of a 

 former igneous action, which I believe to have been incalculably more 

 powerful, not only because it is on the same band or its subordinate 

 parallels that the copious masses of plutonic rocks of this tract and 

 the adjacent mineralized strata occur, but because this line is abso- 

 lutely coincident with the axis of the Carrara and other marbles and 

 their associated slates and crystalline rocks of the Apuan Alps. 

 Now, as those lofty masses or western Apennines, together with their 

 lower parallels in the Gulf of La Spezia, have been shown to be sim- 

 ply altered strata of Jurassic age* ; so in extending our observation in 

 the same line further to the N. and by W., we find that serpen- 

 tinous rocks have there, as in the Tuscan INIaremma, burst through 

 alberese and macigno and in much greater volume. In truth, the 

 copious serjientines and their accompaniments in and around the 

 territory of Genoa, have con'Nerted the cretaceous strata into rocks 

 having all the appearance of palaeozoic slates and flagstones. Other 

 and posterior movements have there also affected, though for the 

 most part mechanically, the contiguous conglomerates and sandstones 

 of miocene age, which on the sides of the pass leading from Genoa 

 to Alexandria occupy very highly inclined positions. The phse- 

 nomena in the Genovesato and Piedmont, like those in the Tuscan 

 Maremmaf, indicate that such beds of the middle tertiary age, 

 whether marine or freshwater, have been dislocated along those lines 

 of disturbance, which at an antecedent period had been marked by 

 the protrusion of the serpen tinous rocks in a molten state. In other 

 words, it was by the post-eocene eruption, that the great metam.or- 

 phosis of the pre-existing strata was caused. A long period of com- 

 parative repose followed, one of the earliest operations of which was 

 the accumulation of miocene conglomerates, for the most part made 

 up of strata previously altered by the serpentine eruptions ; as seen 

 in the hills north of Genoa and Savona on the one hand, or in the 

 Monferrato (Superga) on the other. Another powerful disturbance 

 subsequently took place, when these miocene beds were thrown upon 

 their edges, or were fractured and highly inclined along the same 

 general lines of fissure, which had been marked by a more intensely 

 igneous activity in the previous or serpentine period. 



Although the phsenomena chiefly treated of in this memoir have 

 reference to a great band of cUsturbance proceeding on the whole from 

 N.N.W. to S.S.E. along a length of about 100 miles and a breadth 

 of about 25 miles, a glance at the geological map of Italy by Col- 

 legno, combined with my knowledge of the country, has led me to 

 think, that whilst this line of eruption contains within itself minor 

 parallels, there are other and divergent lines, along which similar 

 strata have been affected by the same eruptive rocks. The country 

 of North-western Italy, which comprehends the Genovesato and the 



* See Quart. Journ. Geol. Soc. vol. v. p. 266 ef seq. 



t See former Memoir and Section Quart. Journ. Geol. Soc. vol. v. p. 283 to 292. 



