Ch. XXXVII] OF THE SWISS ALPS. 613 



rocks. _ In that case the date of their origin would have been thrown back 

 to an area antecedent to the deposition of the Lower Silurian or Cam- 

 brian strata, although in reality they were formed in the Oolitic period, 

 and altered at some subsequent 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 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 fossiliferous and older second- 

 ary formations disappear, and the Cretaceous, Oolitic, Liassic, and at 

 ' some points even the Eocene strata, graduate insensibly into metamor- 

 phic 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 secondary, 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 converted in the same region into crystal- 

 line 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 conviction. 

 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 num- 

 mulitic 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 extent. 



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

 ary and even tertiary strata, which have assumed that semi-crystalline 

 texture which Werner called transition, and which naturally led his fol- 

 lowers, 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. 93.) Now, it is probable that these strata 

 have been affected, although in a less intense degree, by that same plu- 

 tonic action which has entirely altered and rendered metamorphic so 

 many of the subjacent formations ; for in the Alps, this action has by 

 no means been confined to the immediate vicinity of granite. Granite, in- 

 deed, and other plutonic rocks, rarely make their appearance at the sur- 

 face, notwithstanding the deep ravines which lay open to view the 

 internal structure of these mountains. That they exist below at no 

 great depth we cannot doubt, and we have already seen (p. 569) that at 

 some points, as in the Valorsine, near Mont Blanc, granite and granitic 



