Ch. XXXVE.] NORTHERN APENNINES. 759 



the same stratum ; one, where the rock has been in contact with a 

 volcanic or plutonic mass, and has been changed into marble or horn- 

 blende-schist, and another not far distant, where the same bed remains 

 unaltered and fossiliferous ; but when we have to compare two por- 

 tions of a mountain chain — the one metamorphic, and the other un- 

 altered — all the labor and skill of the most practised observers are 

 required, and may sometimes be at fault. I shall mention one or two 

 examples of alteration on a grand scale, in order to explain to the 

 student the kind of reasoning by which we are led to infer that dense 

 masses of fossiliferous strata have been converted into crystalline 

 rocks. 



Northern Apennines — Carrara. — The celebrated marble of Carrara, 

 used in sculpture, was once regarded as a type of primitive limestone. 

 It abounds in the mountains of Massa Carrara, or the " Apuan Alps," 

 as they have been called, the highest peaks of which are nearly 6000 

 feet high. Its great antiquity was inferred from its mineral texture, 

 from the absence of fossils, and its passage downwards into talc-schist 

 and garnetiferous mica-schist; these rocks again graduating down- 

 wards into gneiss, which is penetrated, at Forno, by granite veins. 

 Now the researches of MM. Savi, Boue, Pareto, Guidoni, De la 

 Beche, Hoffmann, and Pilla have demonstrated that this marble, once 

 supposed to be formed before the existence of organic beings, is, in 

 fact, an altered limestone of the oolitic period, and the underlying 

 crystalline schists are secondary sandstones and shales, modified by 

 plutonic action. In order to establish these conclusions, it was first 

 pointed out, that the calcareous rocks bordering the Gulf of Spezia, 

 and abounding* in oolitic fossils, assume a texture like that of Carrara 

 marble, in proportion as they are more and more invaded by certain 

 trappean and plutonic rocks, such as diorite, euphotide, serpentine, 

 and granite, occurring in the same country. 



It was then observed that, in places where the secondary forma- 

 tions are unaltered, the uppermost consist of common Apennine lime- 

 stone with nodules of flint, below which are shales, and at the base of 

 all, argillaceous and siliceous sandstones. In the limestone fossils are 

 frequent, but very rare in the underlying shale and sandstone. Then 

 a gradation was traced laterally from these rocks into another and 

 corresponding series, which is completely metamorphic; for at the top 

 of this we find a white granular marble, wholly devoid of fossils, and 

 almost without stratification, in which there are no nodules of flint, 

 but in its place siliceous matter disseminated through the mass in the 

 form of prisms of quartz. Below this, and in place of the shales, are 

 talc-schists, jasper, and hornstoue ; and at the bottom, instead of the 

 siliceous and argillaceous sandstones, are quartzite and gneiss.* Had 



* See notices of Savi, Hoffimann, and others, referred to by Boue, Bull, de la 

 Soc. Geol. de France, torn. v. p. 317 ; and torn. iii. p. 44 ; also Pilla, cited by Mur- 

 chison, Quart. Geol. Journ., vol. v. p. 266. 



