President of the Geological Society for 1850. 23 



paroxysmal downthrow of overlying rocks. On the contrary, 

 every hypothesis seems to proceed on the assumption that 

 the crystallization of granite was an extremely gradual pro- 

 cess. Many very instructive speculations on this head will 

 be found in the writings of Scheerer, Frapolli, Fournet, 

 Durocher, De Beaumont, and others, who have attempted to 

 explain the reciprocal penetration of the crystals of quartz 

 and felspar which enter into the composition of granites. 

 These minerals, as is well known, have crystallized in an 

 order independent of their relative fusibility, the quartz not 

 only imprinting its form on the felspar, but sometimes itself 

 receiving the imprint of the crystals of felspar. Gaudin and 

 Fournet, in order to account for this fact, have shewn that 

 dissolved flint may cool without solidifying, and remain in a 

 gelatinous state, and thus crystallize after the felspar and 

 mica ; while M. de Beaumont has suggested that electric 

 action may prolong the duration of the viscosity of silex.^ 



The conglomerate of the molasse called nagelflue, before 

 alluded to, and referred to the miocene, if not in part at least 

 to a still later (pliocene) dat^, attains in some places a truly 

 wonderful thickness, exceeding 6000 and even 8000 feet. It 

 is very conspicuous in the Rigi and in the neighbourhood of 

 Lucerne, as well as in the Speer near Wesen. The lower 

 part of the group, containing terrestrial plants, fluviatile 

 shells, and the bones of extinct land-quadrupeds, is considered 

 by M. Escher as a freshwater formation, while some of the 

 sandstones and marls of the upper members of the series con- 

 tain marine shells. f To explain the origin of such a succes- 

 sion of pebbly strata, we are naturally referred, by Studer, 

 Escher, Sir R. Murchison, and others, to a long-continued 

 depression^ along the whole external northern face of the 

 Alps. Numerous torrents are supposed to have issued from 

 the islands which then occupied the site of the loftiest por- 

 tions of the chain, and the continuity of the strata is explained 

 by imagining them to have accumulated on a shelving shore 

 like that of the present maritime Alps. At first the materials 



* Bulletin, 2d Series, vol. iv. p. 1022. 

 t Murchison, ibid. p. 229. 



