ANNIVERSARY ADDRESS OF THE PRESIDENT. ll 



slowly as the growth of a tree or the swelling of its roots in the 

 soil. 



M. de Beaumont, in his essay on volcanic and metalliferous ema- 

 nations*, observes that, according to the experiments of Deville, the 

 contraction of granite in passing from a melted or plastic to a solid 

 state must be more than ten per cent. We have here then at our 

 command an abundant source of depression on a grand scale at every 

 geological period in which granitic rocks have originated. All mine- 

 ralogists seem agreed that the passage from a hquid or pasty to a 

 solid and crystalline state cannot, in such cases, have been instantaneous 

 throughout voluminous masses ; yet by suddenly crystallizing alone 

 could it have given rise to the paroxysmal downthrow of overlying 

 rocks. On the contrary, every hypothesis seems to proceed on the 

 assumption that the crystallization of granite was an extremely gra- 

 dual process. Many very instructive speculations on this head will 

 be found in the writings of Scheerer, FrapoUi, Fournet, Durocher, 

 De Beaumont, and others, who have attempted to explain the reci- 

 procal penetration of the crystals of quartz and felspar which enter 

 into the composition of granites. These minerals, as is well known, 

 have crystalHzed in an order independent of their relative fusibility, 

 the quartz not only imprinting its form on the felspar, but some- 

 times itself receiving the imprint of the crystals of felspar. Gaudin 

 and Fournet, in order to account for this fact, have shown that dis- 

 solved 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 dura- 

 tion of the viscosity of silex f. 



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) date, 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 contain 



* Bulletin de la Soe. Geol. 2nd Series, vol. iv. p. 1312. 

 t Bulletin, 2nd Series, vol. iv. p. 1022. 



