President of tlie Geological Society for 1850. 11 



and in one or more tracts even the tertiary, some of the 

 strata called flysch being converted into a crystalline state.*" 

 Instances are also adduced in the Bernese Alps (by the same 

 author) of bands of granite or granitic schists in the midst 

 of the flysch, demonstrating that the action of heat and 

 vapours, or the causes commonly called plutonic, have 

 changed even these modern deposits into gneiss, as well as 

 into quartz rock and mica schist-t 



To whatever geological period we may be disposed to as- 

 sign the first origin or crystallization of the talcose granite 

 and gneiss of Mont Blanc and other parts of the central 

 nucleus of the Alps, we cannot doubt that they broke through 

 the crust, and were protruded into the atmosphere, or were 

 laid bare by denudation, after the nummulitic limestone was 

 formed, and consequently after the beginning of the eocene 

 period. For my own part, I have little doubt that these 

 granites are all tertiary, and that they may even have passed 

 from a fluid or semifluid state to their present form at an 

 epoch more modern than the eocene period. But although it 

 is only in a few narrow strips of country, like the Central 

 Alps, that nature discloses to us some of the nether-formed 

 rocks of such modern geological eras, we cannot doubt that 

 still greater modifications of the interior have extended down- 

 wards for many miles or leagues in depth beneath the Alps, 

 and beneath every region, whether of land or sea, which has 

 risen, sunk, or oscillated in level since the fossil shells and 

 zoophytes of the lower eocene period were living in the sea. 

 The imagination of the geologist strives in vain to form a 

 just conception of the extent of these internal modifications 

 of the crust, of which we are only beginning to interpret the 

 outward signs. How much fracture and dislocation of solid 

 rock must have taken place ! how much heating and cooling, 

 expansion and contraction, drying and baking, softening and 

 re-solidifying of sedimentary strata ! Over how vast an 

 area, and to how great a depth, often hundreds of yards or 



* Quart. Journ. of Geol. Soc., vol. v. p. 164. 

 t Ibid. vol. V. p. 213. 



