MINERALIZED AND METHYLOSED ROCKS. 31 



We certainly cannot admit that ct later sediments " are with- 

 out alkalies ; for there are several known cases which testify to 

 the contrary : one, the Taunus slates, contains a large amount 

 of alkalies, ( ' more even than some crystalline rocks, such as 

 trachyte, syenite, granite, &c. " *. However, admitting for the 

 moment that these "later sediments" were originally deficient 

 in alkalies, and that in their altered form they contain horn- 

 blende with feldspar, mica, and other alkaliferous minerals, we 

 may be permitted to ask What constitutes the force of the last 

 argument? If such minerals can be generated in "later sedi- 

 ments " that have undergone " local alteration " by " hydro- 

 thermal action," Why cannot the same action have generated 

 the te identical " minerals which characterize the Archseans of 

 Canada and other regions ? 



As to the contention that the examples of " later sediments " 

 are nothing more than "local," we do not understand how 

 Sterry Hunt (admitting some of the examples to which he may 

 be referring to be such) can set aside the contrary testimony of 

 the most eminent field geologists (Elie de Beaumont, Bonnard, 

 Froisset, Studer, Delesse, &c.) that in France and Switzerland 

 there are Palaeozoic, Triassic, and Jurassic rocks, occupying wide 

 regions, which have been converted into arkoses, crystalline 

 schists, and other rocks containing oligoclase, damourite, sericite, 

 and some other minerals, all of which are rich in alkaline con- 

 stituents. 



It may be, as contended by Gastaldi, Wick, and Baretti, 

 that there are gneisses and various crystalline rocks of pre- 

 Cambrian or pre-Silurian (Archaean) age in the region of the 

 Central Alps. The same may be admitted for the " pre- Carboni- 

 ferous " gneisses in the Mont-Cenis district. But it does not 

 necessarily follow that there are no rocks of the kind belong- 

 ing to the Palaeozoic and Mesozoic periods in the same areas. 



Because Alphonse Favre has detected a specimen pronounced 

 to belong to " Eozoon Canadense " in the " calcaire crys- 

 tallise associe avec serpentine enclavee dans le gneiss " in the 

 ravine of the Mettenbach on the flanks of the Jungfrauf, Sterry 



* Bischof, op. cit. vol. iii. p. 129. 



t Rapport sur les travaux de la Societe de Physique el d'Histoire uatu- 

 i-elle de Geneve de Juiu 1866 a Mai 1867, p. 282. 



