760 METAMORPHIC ROCKS OF SWISS ALPS. [Ch. XXXVII. 



these secondary strata of the Apennines undergone universally as 

 great an amount of transmutation, it would have been impossible to 

 forma conjecture respecting their true age; and then, according to 

 the method of classification adopted by the earlier geologists 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 de- 

 position of the Lower Silurian or Cambrian strata, although in reality 

 they were formed in the Oolitic period, and altered at some subse- 

 quent and perhaps much later 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 fossil- 

 iferous 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 fossilifer- 

 ous and older secondary formations disappear, and the Cretaceous, 

 Oolitic, Liassic, and at some points even the Eocene strata, graduate 

 insensibly into metamorphic rocks, consisting of granular limestone, 

 talc-schist, talcose-gneiss, micaceous schist, and other varieties. In 

 regard to the age of this vast assemblage of crystalline strata, we can 

 merely affirm that some of the upper portions are altered newer sec- 

 ondary, and some of them even Eocene deposits ; but we cannot avoid 

 suspecting that the disappearance both of the older secondary and 

 primary fossiliferous rocks may be owing to their having been all con- 

 verted in the same region into crystalline schist. 



It is difficult to convey to those who have never visited the Alps 

 a just idea of the various proofs which concur to produce this con- 

 viction. In the first place there are certain regions where Oolitic, 

 Cretaceous, and Eocene strata have been turned into granular marble, 

 gneiss, and other metamorphic schists, near their contact with granite. 

 This fact shows undeniably that plutonic causes continued to be in 

 operation in the Alps down to a late period, even after the deposition 

 of some of the nummulitic or middle Eocene formations. Having 

 established this point, we are the more willing to believe that many 

 inferior fossiliferous rocks, probably exposed for longer periods to a 

 similar action, may have become metamorphic to a still greater ex- 

 tent. 



We also discover in parts of the Swiss Alps dense masses of sec- 

 ondary and even tertiary strata which have assumed that semi-crys- 

 talline texture which Werner called transition, and which naturally led 

 his followers, who attached great importance to mineral characters 

 taken alone, to class them as transition formations, or as groups older 

 than the lowest secondary rocks. (See p. 88.) Now, it is probable 

 that these strata have been affected, although in a less intense degree, 

 by that same plutonic action which has entirely altered and rendered 

 metamorphic so many of the subjacent formations ; for in the Alps, 



