296 



LYELL'S ELEMENTS OF GEOLOGY. 



Age of Metamorphic Rocks of the Swiss Alps. 



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 

 estabHsh these conclusions it was first pointed out, that the cal- 

 careous 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 trap- 

 pean and plutonic rocks, such as diorite, euphodite, serpentine, 

 and granite, occurring in the same country. 



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

 ations are unaltered, the uppermost consist of common Apen- 

 nine limestone 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. Now a gradation has been 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 siHceous 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 hornstone ; and at the bottom, instead 

 of the siliceous and argillaceous sandstones, are quartzite and 

 gneiss.* Had these secondary strata of the Apennines under- 

 gone universally as great an amount of transmutation, it would 

 have been impossible to form a conjecture respecting their true 

 age and then, according to the common method of geological 

 classification, they would have ranked as primary rocks. In that 

 case the date of their origin would have been thrown back to an 

 era antecedent to the deposition of the Lower Cambrian strata, 

 although in reality they were formed in the oolitic period, and 

 altered at some subsequent and unknown epoch. 



Alps of Switzerland. — In the Alps, analogous conclusions 

 have been drawn respecting the alteration of strata on a still 

 more extended scale. In the eastern part of that chain, some 

 of the primary fossiliferous strata, as well as the older secondary 

 formations, together with the oolitic and cretaceous rocks, are 

 distinctly recognizable. Tertiary deposits also appear in a less 

 elevated position on the flanks of the Eastern Alps ; but in the 

 Central or Swiss Alps, the primary fossihferous, and older second- 

 ary formations disappear, and the cretaceous, oolitic, and liassic 

 strata graduate insensibly into metamorphic rocks, consisting of 



* See notices of Savi, Hoffman, and others, referred to by Boue, Bull, de la Soc. 

 G^ol. de France, torn. v. p. 317. and torn. iii. p. 44. 



